I've been devouring web novels for some time now, so I have a pretty wide experience (within my preferred genres).  My preferences probably won't match many of yours, but I figured I would make some recommendations like I used to with visual novels.

Isekai'd+Overpowered/cheat protagonist

Death March Kara Hajimaru Isekai Kyousoukoku (https://ncode.syosetu.com/n9902bn/)- Despite the anime being a flop, this is easily one of the best fantasy web novel series of the type.  In addition, the LN version differs so greatly from the web novel that you can actually enjoy them completely separately from one another, which makes them double the fun.  

Arifureta Shokugyou de Sekai Saikyou (https://ncode.syosetu.com/n8611bv/)- Yes, the anime was mostly crap (except for Yue being a vampire goddess), but the web novel is awesome.  It was also something of a trendsetter, setting the gold standard for the 'betrayed protagonist rises to be the strongest' trope.  The web novel has a huge advantage over the light novel series in that the after-story (which is now longer than the original story) is godly and immensely fun to read.

My Classmates were Summoned to Another World but I was Reincarnated (https://kakuyomu.jp/works/16816452221074480581)- Basically, the protagonist dies during the summoning and gets reincarnated as a true vampire by the ditzy goddess of the world her classmates were summoned to and goes on a self-indulgent journey/adventure/rampage across the surface of the other world.  The protagonist is definitely chaotic neutral in personality, though her actions often split off into chaotic good and chaotic evil depending on who she is dealing with.  For people who want to laugh at a protagonist's absolutely insane antics, this is a good choice.

Isekai ni Houchi-ge Riron o Mochikondara Isekai Saikyou ni Nareru Isetsu (https://kakuyomu.jp/works/16817330652291194063)-  Basically a gamer gets reborn into a rather harsh and massive fantasy isekai, where he uses sorcery to create autonomous spells that go around killing monsters so he can level up faster.  He is a leveling addict and this story, like most of this author's stories, is full of insane characters (including the protagonist and heroine).  This is one of the few male protagonist WN series I've met that doesn't include a harem.

Toriaezu Shinu Wa (https://kakuyomu.jp/works/16816700427424058338)- Made by the same author as Houchi-ge, it was his pilot work.  It is complete (this author follows through and consistently posts his works, so you don't need to worry about fade-outs), so you can just dive in and read from the beginning to the end.  In this one, the protagonist and his class get summoned to another world, and when he finds out some of his nastier classmates intend to assassinate him, he uses the plot to get out of town (faking his death) and gain his freedom.  This one is pretty dark, the protagonist actively committing genocide and purges against religion (though the religion deserves it), and his girlfriend is a psychotic yandere who is incapable of empathy for anyone but him.  However, the character personalities in this one are really well presented, which matches this author's style.

Paradigm Parasite (https://kakuyomu.jp/works/1177354054891938248)- Protagonist is reborn as a parasite that possesses the corpse of a young noble and proceeds to rampage across the psychotic isekai he ended up in.  He is utterly cold-blooded, pragmatic, and predatory by nature.  This is a pure chaotic evil protagonist acting on his worst instincts throughout much of the story.

Isekai'd+Adventurer/Not overpowered

Jiriki de Isekai he! (https://kakuyomu.jp/works/1177354054941828435)-  By coincidence, the protagonist manages to create a magic circle that transports him to another world... by killing him.  The god who greets him informs him that his actions count as suicide, thus he won't be granted any special rewards.  He is reborn as an orphan and regains his memories by accident, his skill (not a cheat skill) activating for the first time as a result of a near-death experience.  He sets out to become an adventurer, living his isekai life as best he can.  This series is complete, so you can just dive in and read it from beginning to end.

Karyoku no Nai Kaze Mahoutsukai wa, Isekai nite Ken de Mau (https://kakuyomu.jp/works/16817330652107435856)- An excellent story for those who want a reincarnated protagonist who isn't overpowered and lives his life as an adventurer.  The protagonist is half-halfling, half-giant in a world that is a half-step away from the age of mythology.  

Annainin wa Isekai no Jukai o Samayou (https://kakuyomu.jp/works/1177354054918935123)- Protagonist falls through a gate to another world and is forced to become an adventurer in order to survive.  Eventually, he is able to return to Earth and becomes a 'guide', teaching people how to survive on the other world.  

Modern Fantasy/dungeons (sometimes with an isekai'd then returned protagonist)

Isekai Kara Kikan Shitara Chikyuu ga Fantasy Deshita. Ato, Make Heroine domo, Kocchi Minna (https://kakuyomu.jp/works/16817330650225915619)- This one focuses on a protagonist who succeeds in killing the evil god in another world and returns to earth, only to once again face his childhood friend presenting his newest lover to him with a victorious expression.  However, he doesn't care at all, as he is finally free of the hell of the other world! (He really, really hates the isekai).  This series is mostly humorous as Nacchan's manic personality and immense power meets Earth's fantasy beings in clashes that are usually disastrous for the fantasy beings.  

Shachiku Kensei, Haishinsha ni Naru (https://kakuyomu.jp/works/16817330657186803576)- Mix of dark humor and overpowered action as a guy in a business suit explores the depths of dungeons.  It is updated irregularly but even just what is there so far is worth reading.

Seikatsu Mahoutsukai no Gekokujou (https://kakuyomu.jp/works/16816452218254294002)- Oppressed protagonist with a gift for the weakest school of magic discovers the sage system for his school of magic and develops it for combat, eventually becoming a famous dungeon crawler and magic developer.  Series is complete and the battles are pretty cool.  While technically the protagonist is overpowered, that is because he works hard at it and discovers ways to deal with the situations he encounters.

Maou o Taoshite Gendai ni Kaetekitara Parallel World Deshita! (https://kakuyomu.jp/works/1177354054888599901)- An overpowered isekai protagonist returns to earth with his divine fox lover, only to find that he returned to a parallel world where dungeons emerged during WWII.  The story is mostly ecchi+action+people being people.  The series is complete.

Onmyouji/Youkai/Modern Fantasy

Gendai Onmyouji wa Tensei Lead de Musou Suru (https://kakuyomu.jp/works/16816927863187332284)- The protagonist is reborn into a version of Japan where youkai and onmyouji are still at war with one another and uses his self-awareness to prepare for his future by building up his power young.  Pretty fun to read, still ongoing if slowly so.

Inousha ga Futsuu ni Iru Sekai he Tensei Shitara (https://kakuyomu.jp/works/16816452218603293395)- Protagonist is reborn into what he thinks is a game world in the body of a villain who does pretty horrible things to most of the heroines.  This series is pretty dark, and it becomes evident (through other perspectives) that this isn't actually a game world early on.  The protagonist is technically overpowered, but so are a lot of the enemies and one of the main heroines.  It shows the dark and hard sides of harems and political marriages as well, so for people who want a 'happy harem' story, this isn't a good choice.

Demon Ruler (https://kakuyomu.jp/works/1177354054882154317)- Salaryman protagonist gains access to pocket dimensions where he can take out his daily stress on real monsters and gain money and power.  Quite naturally, he enthusiastically dives into his new hobby.  Fun to read, gets more apocalyptic after a while.

Anata no Tenshoku wa 'Daiyoukai' Desu (https://ncode.syosetu.com/n2559fp/)-  One of my all-time favorites.  The protagonist lives in a future where humanity's population once fell to critical levels and only recovered through the use of the 'oracle' system, which tells people their ideal occupations.  When he uses it, it tells him his ideal occupation is being 'a great youkai', and he is introduced to the real reason why the system exists... to balance the supernatural with the natural.  The protagonist is more than a little crazy, his adopted mother is Tamamo no Mae, his adopted father is Shuten-doji, and his adopted grandfather is Sojou-bou (he is actually descended from all three).  This series has a lot of dark laughter, interesting action, and a few moments that will have you weeping until snot flows out of your nose.  Too bad this author's other works are sub-par at best, lol.

Fantasy, not from Earth

Kami-sama ni Muriyari Ikikaesareta (https://kakuyomu.jp/works/16816452220822010394)-  This begins as the sad tale of a young orphan boy (recently deceased saving a little girl from a wolf) faces the goddess who broke her promise and failed to protect his mother and himself.  As a result, she tries to revive him, but he demands that he be allowed to die, drawing the attention of higher beings, starting a series of events that eventually results in him being granted access to all class skills and resurrected with two divine guardians.  This is not a tale of a guy doing whatever the hell he wants and making a mess of the world.  Rather, it is the tale of a boy who has suffered so much he no longer reacts to the little pains and reacts to others with cold rationality, ignoring most of the social rules in the process.  The protagonist is rather wordy when he thinks someone is doing something wrong, and he has no hesitation about confronting people with it.

Kurotobi no Seija (https://ncode.syosetu.com/n9105fz/)-  Cleric makes a deal with a dark god for power to get back at those who exiled him.  Decent read for those who don't want an Earthling protagonist.