Clephas

Shirogane no Soleil was the first Soleil game and the one that defined the  most essential elements of how the Runes, Valkyries, and other elements were treated within the multiverse (though a lot has been retconned since then).  It is also a very old-style chuunige.  The protagonist starts out as a normie, the girls are more powerful than him, and there is a horrible cost for using their powers.  The heroines will seem somewhat archetypical in comparison to modern chuunige heroines, but that doesn't hurt the game as much as you would think.  If you intend to play other games in the series, you should also pay attention to what happens to the various heroines, as some of it 'ripples' outward through the multiverse and has effects on their alternative versions.  

More like the game that solidified their game style.  While their last seven games all seem different on the surface, they are essentially similar in concept.  Create a situation that is full of open or hidden despair and disaster, make it go bang, then bring on the feels.  Mirai Nostalgia, which came before it, was also like this, if to a lesser degree, but it was more of an experimental than a clearly delineated style template at the time.  Hapymaher has the benefit of the best and most unique soundtrack the company has ever produced, combined with near-perfect music direction.  This enhances a plot that is at times somewhat scatterbrained due to its nature (a dream) and turns it into a kamige. 
The ones that stand out, to me, are Aoi Tori, Amatsutsumi, and Realive, all three of which are more feels-oriented than Chrono Clock or Shiawase Kazoku-bu (which is also good).  These three are helped by having excellent casts of characters and great writing but are hindered by abuse of the ladder-style story structure.  In addition, for some reason Purple Software went for near-generic soundtracks after Hapymaher, a choice I think was a terrible mistake, given the degree to which Hapymaher's atmosphere is defined by its music and music direction (though its VA choices are godly too).
The lack of Morisaki Ryouto and the tendency to split the tasks between multiple writers seems to harm them sometimes, which saddens  me... Morisaki Ryouto is one of the best writers out there, and without him, Purple Soft has developed a tendency to make questionable hiring choices when it comes to its writing staff (why they would hire the writers from Laplacian, I don't understand).  From what I can tell, the two saving graces seem to be that Purple Soft has retained the same BGM composer and Ishikawa Yasushi as the scenario designer and lyrics writer, who seem to work to maintain the same style.

Most people, even Nitroplus fans, consider Gekkou no Carnevale an acquired taste.  I liked it, I liked the themes, and I even liked the fighting.  I didn't like two of the four heroines (ironically, I disliked both of the main heroines, while I liked their respective sub-heroines and their endings).  Like most Nitroplus games, it has sound problems (for some reason, almost all Nitroplus games have 'gaps' between the loops of their BGMs, and it can be jarring when the music cuts out for a second during an important scenes).  
The story in general is too much of a 'chapter in an endless saga' type thing with the beginnings mostly ignored.  The main antagonist on the wolf side is boring, and the one on the doll side is unnecessarily inscrutable.  As such, the game will always remain an acquired taste adored by its fans and disliked by most everyone else.
Edit: to be clear about what I mean by the 'endless saga' comment, the fights between the werewolves and the doll-users.

Only ones I've played (that I remember) are Netotte Megami and Edelweiss.   Netotte Megami was pretty awful, as I recall (nukige with bad h-scenes and almost had a real story, lol).  Edelweiss... I actually played in English, if you could actually call that English.  Edelweiss's first version (1.0) on Mangagamer was a straight-out machine translation with no edit whatsoever.  I actually enjoyed it more when I replayed it in Japanese later, though even then there were so many much better games out there...

AXL doesn't really vary its general formula where it involves heroines that much.  They reuse templates shamelessly, but the games they produce are almost universally enjoyable from beginning to end, which is in itself an accomplishment.  Rather than forcibly evolving their style to perfectly match trends, they've just polished their existing style, making incremental improvements and finding ways to use their existing toolkit more effectively.  AXL is the paragon of doing the same thing in new ways, and so if you have played any AXL game, other AXL games will feel familiar but different, which is surprisingly reassuring, since 'innovation' can become toxic when it goes too far.

Pulltop has been getting crappier every year though... their unwillingness to hire writing talent is sabotaging them.  Natsuiro Recipe was their last truly enjoyable game... 

Haruuru's translation of the Main routes is long-since done.  I was mostly working with @ittaku in an advisory capacity (details, colloquialisms, other stuff that requires a ridiculously long background).  It is true, and we both agree, that the Main route is much, much better than the Branch route.  Not only are Tonoko, Shino, and Miyabi much better heroines, but everything from the protagonist's personality to how the heroines' emotions and characterizations are handled are so dramatically different in quality that there is no possible comparison.  The only real exception is that Yuuna's route has some good drama/story, probably more as a coincidence than anything else (Misaki and Sumika's routes were... basically somewhat above average charage fare at best).  
I don't quite agree with the reviewer in this case, as I always reviewed based on the Main path and ignored the Branch entirely, simply because my first experience of it was enough to put me off permanently.  The Main routes have some truly epic feels, great character interactions, and are the truest to the 'nature' of the school's purpose, which is confinement and segregation from the larger sister school's population and the general population in general.  This is ironic, since the Branch school girls are supposedly more of an 'embarrassment' to their powerful families, whereas the Main School heroines are supposedly only problem children after the fact.  
Perhaps the way the Branch school's writer screwed up the most was that he quite simply didn't manage to match two of the three heroines to the school's purpose.  Neither Misaki nor Sumika had any business being in the Branch school at all, considering that they were both capable and had personalities that were not necessarily 'embarrassing' to their families (in both cases, they are loved deeply and don't have any traumas or major issues that should have resulted in them ending up there).  
Yuuna's route stands out from the other two Branch routes... to a degree that you have to wonder if the same writer had anything to do with it.  It is also the most overtly morally distasteful of the paths (not in the teacher-student relations sense though), which is probably why it has such impact.  Yuuna's presence there also makes a great deal of sense once you've done her path, which is different from the two redheads.
Miyabi's path tends to get deified by fanboys, which I can understand.  Tsukasa's actions, the characters' reactions, and the feels are all so well coordinated that it is impossible not to cry numerous times throughout the path.  However, it needs to be said that both Tonoko and Shino's paths are of the same level of quality, if having someone different tracks (the last part of Shino's path had me rofling, though).

Haruuru's translation of the Main routes is long-since done.  I was mostly working with @ittaku in an advisory capacity (details, colloquialisms, other stuff that requires a ridiculously long background).  It is true, and we both agree, that the Main route is much, much better than the Branch route.  Not only are Tonoko, Shino, and Miyabi much better heroines, but everything from the protagonist's personality to how the heroines' emotions and characterizations are handled are so dramatically different in quality that there is no possible comparison.  The only real exception is that Yuuna's route has some good drama/story, probably more as a coincidence than anything else (Misaki and Sumika's routes were... basically somewhat above average charage fare at best).  
I don't quite agree with the reviewer in this case, as I always reviewed based on the Main path and ignored the Branch entirely, simply because my first experience of it was enough to put me off permanently.  The Main routes have some truly epic feels, great character interactions, and are the truest to the 'nature' of the school's purpose, which is confinement and segregation from the larger sister school's population and the general population in general.  This is ironic, since the Branch school girls are supposedly more of an 'embarrassment' to their powerful families, whereas the Main School heroines are supposedly only problem children after the fact.  
Perhaps the way the Branch school's writer screwed up the most was that he quite simply didn't manage to match two of the three heroines to the school's purpose.  Neither Misaki nor Sumika had any business being in the Branch school at all, considering that they were both capable and had personalities that were not necessarily 'embarrassing' to their families (in both cases, they are loved deeply and don't have any traumas or major issues that should have resulted in them ending up there).  
Yuuna's route stands out from the other two Branch routes... to a degree that you have to wonder if the same writer had anything to do with it.  It is also the most overtly morally distasteful of the paths (not in the teacher-student relations sense though), which is probably why it has such impact.  Yuuna's presence there also makes a great deal of sense once you've done her path, which is different from the two redheads.
Miyabi's path tends to get deified by fanboys, which I can understand.  Tsukasa's actions, the characters' reactions, and the feels are all so well coordinated that it is impossible not to cry numerous times throughout the path.  However, it needs to be said that both Tonoko and Shino's paths are of the same level of quality, if having someone different tracks (the last part of Shino's path had me rofling, though).

Haruuru's translation of the Main routes is long-since done.  I was mostly working with @ittaku in an advisory capacity (details, colloquialisms, other stuff that requires a ridiculously long background).  It is true, and we both agree, that the Main route is much, much better than the Branch route.  Not only are Tonoko, Shino, and Miyabi much better heroines, but everything from the protagonist's personality to how the heroines' emotions and characterizations are handled are so dramatically different in quality that there is no possible comparison.  The only real exception is that Yuuna's route has some good drama/story, probably more as a coincidence than anything else (Misaki and Sumika's routes were... basically somewhat above average charage fare at best).  
I don't quite agree with the reviewer in this case, as I always reviewed based on the Main path and ignored the Branch entirely, simply because my first experience of it was enough to put me off permanently.  The Main routes have some truly epic feels, great character interactions, and are the truest to the 'nature' of the school's purpose, which is confinement and segregation from the larger sister school's population and the general population in general.  This is ironic, since the Branch school girls are supposedly more of an 'embarrassment' to their powerful families, whereas the Main School heroines are supposedly only problem children after the fact.  
Perhaps the way the Branch school's writer screwed up the most was that he quite simply didn't manage to match two of the three heroines to the school's purpose.  Neither Misaki nor Sumika had any business being in the Branch school at all, considering that they were both capable and had personalities that were not necessarily 'embarrassing' to their families (in both cases, they are loved deeply and don't have any traumas or major issues that should have resulted in them ending up there).  
Yuuna's route stands out from the other two Branch routes... to a degree that you have to wonder if the same writer had anything to do with it.  It is also the most overtly morally distasteful of the paths (not in the teacher-student relations sense though), which is probably why it has such impact.  Yuuna's presence there also makes a great deal of sense once you've done her path, which is different from the two redheads.
Miyabi's path tends to get deified by fanboys, which I can understand.  Tsukasa's actions, the characters' reactions, and the feels are all so well coordinated that it is impossible not to cry numerous times throughout the path.  However, it needs to be said that both Tonoko and Shino's paths are of the same level of quality, if having someone different tracks (the last part of Shino's path had me rofling, though).

Chanter is your standard old-style charage... and a kusoge.
Shuumatsu Shoujo is one of my favorites and a game I recently reviewed (relatively speaking).  For my full thoughts:
 
On a female friend's recommendation, I tried to play Lamento, but I lost interest fairly quickly... BL games' conventions make me sigh with exasperation even more than the ones in charage/moege.
Extravaganza I made an attempt to play early in my VN-reading 'career'... and let's just say, it takes a peculiar set of tastes to enjoy anything by Black Cyc, but it takes especially peculiar tastes to enjoy Extravaganza.
 
 

Kono ko ga Itara is a good charage, though not kamige material.
Kikaijikake no Eve has a decent story and horrible gameplay.

Silverio is easier than Dies Irae, but not that much easier.  As I mentioned above, it is heavy on exposition.  However, Takahama and the others are less obsessed with poetic turns of phrase than Masada is, so it is marginally easier to read.

Of these, I've played Kaiware and Maid-san...
Maid-san is... predictably a maid-themed nukige that happens to include swords.  I couldn't fap to it, so that should say everything that needs to be said about it, since it is a nukige.
Kaiware is a kusoge.  It was among a plethora of random games I played through at the time.  While I do have a mild gender-swap fetish, this was one of the few games where a rather abortive effort was made to take it seriously.  It failed.  

I played Kanojo-tachi no Ryuugi... like most games by that company, the relationships are twisted and incestuous, with a lot of surprising drama despite many of the characters being mostly straightforward.  
Iinchou wa Shounin-sezu bored me to death... it was sort-of funny for the first part of the game, but the actual romantic portion is worse than most moege.
H20 is pretty overrated... people kept trying to get me to play it, but I couldn't get into it.
 

Voiced protagonist is obvious.  It shouldn't even need mentioning that having the protagonist voiced is a universal plus.  By definition, point 2 is a quality that allows a protagonist to be 'not just another worthless non-person protagonist', so again, a plus.   In my opinion, if the heroines are voiced in ANY VN, the protagonist should also be voiced... but if you like your protagonist to be a non-person cipher with no personality, that's your business.  
Point 3 is purely personal tastes, I'll admit openly.  However, it is a commonality to all good trap protag charage.  Probably because most ojousama protagonists in JVNs tend to fall into the yurufuwa (think sweet-mannered airhead), arrogant (often combined with tsundere elements, for some reason), or elegant archetypes, all of which are good archetypes for creating atmosphere.  
Point 4... completely glossing over the drama of a cross-dressing revelation stretches suspension of disbelief by definition, even beyond that of a cross-dressing guy infiltrating a girls' school.  While no one seriously thinks any of this is realistic, suspension of disbelief for the purpose of enjoyment is a necessary process to enjoy most fiction.  Oh, I'm not talking about drama on the level of Tsuki ni Yorisou Otome no Sahou's normal/bad end, but rather the kind of drama where there is real tension on one or both sides of the equation.  In my experience, when all or a majority of the heroines sort of just blink and say 'that's fine' without even thinking about it, it is a serious mood-killer.
5.  This is just a common comedic point that creates internal laughs for fans of the genre... and having built-in jokes is always nice.  
In the end, points 1, 2, and 4 contribute the most to the quality of the works in question.  3 and 5, as you mentioned, are mostly matters of taste and commonality.  
Well, if you actually wanted an answer, there is your answer.

Voiced protagonist is obvious.  It shouldn't even need mentioning that having the protagonist voiced is a universal plus.  By definition, point 2 is a quality that allows a protagonist to be 'not just another worthless non-person protagonist', so again, a plus.   In my opinion, if the heroines are voiced in ANY VN, the protagonist should also be voiced... but if you like your protagonist to be a non-person cipher with no personality, that's your business.  
Point 3 is purely personal tastes, I'll admit openly.  However, it is a commonality to all good trap protag charage.  Probably because most ojousama protagonists in JVNs tend to fall into the yurufuwa (think sweet-mannered airhead), arrogant (often combined with tsundere elements, for some reason), or elegant archetypes, all of which are good archetypes for creating atmosphere.  
Point 4... completely glossing over the drama of a cross-dressing revelation stretches suspension of disbelief by definition, even beyond that of a cross-dressing guy infiltrating a girls' school.  While no one seriously thinks any of this is realistic, suspension of disbelief for the purpose of enjoyment is a necessary process to enjoy most fiction.  Oh, I'm not talking about drama on the level of Tsuki ni Yorisou Otome no Sahou's normal/bad end, but rather the kind of drama where there is real tension on one or both sides of the equation.  In my experience, when all or a majority of the heroines sort of just blink and say 'that's fine' without even thinking about it, it is a serious mood-killer.
5.  This is just a common comedic point that creates internal laughs for fans of the genre... and having built-in jokes is always nice.  
In the end, points 1, 2, and 4 contribute the most to the quality of the works in question.  3 and 5, as you mentioned, are mostly matters of taste and commonality.  
Well, if you actually wanted an answer, there is your answer.

The best trap protags are of that type... though there are a few that make a good pass as 'predators in skirts' types (Ojousama no Hanbun wa Ren'ai de Dekiteimasu).  Mizuki in this one and Tsuki ni Yorisou Otome no Sahou's protag are the best outright.  It really is too bad that Otome no Sahou's sequel based off the Luna ending (protagonist is submissive version) sucked so badly.  The cross-dressing son started out really well, but the heroine routes ruined things, because his personality changed the second the routes started.  There are also weren't any really stand-out heroines.

This is another one I played way back when.  Like most chuunige from the early era (2000-2008) it has a tendency to be obscure, and the protagonist (abilities, personality, etc) doesn't quite fit with the setting.  However, for lovers of guro and psycho heroines this is a good game, and it is a great deal darker in a visceral sense than many later works.  For people who like guro and dark stuff but don't want to go as far as Clock-up's disgusting games, this is actually a pretty good choice.  I forgot about it mostly because it isn't a game that I would want to replay over and over...

Basically, it is a theoretical where there was official acknowledgement of Japan having multiple ethnicities early on (think right after WWII) instead of relatively recently (Japan only acknowledged the existence of the Ainu and a few other ethnicities in the last twenty years or so).  This resulted in a social movement, where people migrated to areas with people of the same ethnicity, and this caused a degree of political alienation between them that eventually split the nation politically in a way that is eerily familiar to anyone who has been watching the Brexit mess or American politics. 
Tbh, Gunjou no Sora tries too hard to be an intellectual VN and falls somewhat short of making its objectives and themes clear.  The decision to resort to using the child soldiers trope (the protagonist and friends) was an even poorer choice, as it muddled things, distracting from the central themes.
Typical of Light, the writing quality is high, but it is one of their few failures to match the results to their own pretentiousness, lol.
Edit: Until relatively recently in history, the cultural unity between the people of Kyushu, Shikoku, Hokkaido, and Honshu...  and Okinawa of course were limited.  Each has their own cultural elements that aren't present in the same forms as the others.  However, back during the Meiji Restoration era, the unification of official Shinto beliefs was used to force cultural homogeneity on the more traditionally 'different' groups.  The Ainu, who actually had their own language and dramatically different culture, suffered the most from this, actually going into direct conflict with the 'wajin' several times in the nineteenth and early twentieth centuries. 

I was discussing this with a friend recently, but it was our consensus that Maggot Baits is one of the few eroge that could benefit from having all its h-scenes removed...  To be blunt, the h-scenes are in the way (vanilla or evil h, it doesn't matter).  
As for pacing, that's actually typical of Kurashiki when he doesn't have Takahama, Marimo, or one of his other Light people keeping him from doing what he wants.  Sora no Baroque had a similar problem.  The writing is good, the story is good, but the pacing is abominable.
Edit: I liked the game's story, but the H was gratuitous in several negative ways (understatement).

I was discussing this with a friend recently, but it was our consensus that Maggot Baits is one of the few eroge that could benefit from having all its h-scenes removed...  To be blunt, the h-scenes are in the way (vanilla or evil h, it doesn't matter).  
As for pacing, that's actually typical of Kurashiki when he doesn't have Takahama, Marimo, or one of his other Light people keeping him from doing what he wants.  Sora no Baroque had a similar problem.  The writing is good, the story is good, but the pacing is abominable.
Edit: I liked the game's story, but the H was gratuitous in several negative ways (understatement).

I was discussing this with a friend recently, but it was our consensus that Maggot Baits is one of the few eroge that could benefit from having all its h-scenes removed...  To be blunt, the h-scenes are in the way (vanilla or evil h, it doesn't matter).  
As for pacing, that's actually typical of Kurashiki when he doesn't have Takahama, Marimo, or one of his other Light people keeping him from doing what he wants.  Sora no Baroque had a similar problem.  The writing is good, the story is good, but the pacing is abominable.
Edit: I liked the game's story, but the H was gratuitous in several negative ways (understatement).

This was my first untranslated VN, so my impression differs somewhat.
1.  This was the first game where I discovered that h-scenes could be hilarious.  For some reason, Kaze no Ushiro ni Ayumu Mono's (yes, that's her name) h-scene hit my funny bone and made me rofl.
2.  The protagonist is not at the highest tiers for me either, but he has good reason for being the way he is.
3.  One interesting impression I felt needs to be noted is that the inhuman in this game (thus the first part of the title, Jingai) are fundamentally inimical to humans and humans are inimical to them.  In addition, it is possible for humans to transition into Jingai through cross-contamination, which is partly physical but can also be a spiritual change (it should be noted that both are explored as part of the VN).
4.  This game was never actually completed (or so goes the story).  There was supposed to be a remake, but it never happened... probably because Nitroplus is so slow on everything that it got canceled.
5.  There are multiple, drastically different endings to each of the three heroine paths.  These endings are interesting to explore, but the common element all of them is that all of them are bittersweet at best.
6.  Story-wise, this game's most negative point is one that is actually common to more than half of all Nitroplus game... deliberate obscurity. 
7.  The heroines in this game are... unique.  None of them have purely human perspectives, and that becomes ever more obvious as the story progresses.

This game had decent action scenes, a good story, and horrible sex scenes (except from the perspective of Clock-up fans).  I played it relatively early on in my untranslated 'career', and I remember being a little disgusted at how hard it was to figure out how to get to the various endings, even WITH a walkthrough.  The twins are obviously the best heroines and endings relating to them are generally the most interesting... with the infected vampire hunter girl's endings coming a close second.  However, as a whole, the game tended to lack cohesion due to the way progression is handled. 

A 'coworker?'  Well, really a subcontractor I introduced to VNs about a year ago... He isn't particularly brilliant (if anything, he's on the downward side of human intelligence), but he's been a bookworm as long as I've known him (about twelve years now?). I gave him a copy of Dies Irae and he managed to finish it in about forty hours (the English version).  He was also able to have a decent conversation on the events that occurred and seemed to grasp most of the twists.  Part of that comes from him being a fiction specialist normally, but it is also proof of concept.  He did miss some things, but then, very few people grasp every single nuance of what happens in that game the first time around (I certainly didn't).