I just 100%'d Rabi-Ribi, and I must say it was a very rich experience
On the surface it just seems like a brainless 2D platformer with cute grills slapped on top to lure some horny teenagers, but if you look beneath the surface you'll find something truly special.
Firstly, the controls are crisp, and making mistakes feel like your mistake, not the game's.
The metroidvania aspect of the game is really greatly made: The secrets are usually something that you wouldn't find just straddling about, you have to look for them, but only a minor part of them are truly "hard to find", in the truest sense. As you explore the different plains, you get many possible detours and such, which gave a nice, fresh feel to the game. There truly is three major expeditions you can make, after high jump, after slide and double jump, and after air dash. On these every single expeditions you'll find lots of new places to discover, great amounts off items, and more bosses. All of this is made brilliantly. Even the pacing between these power-ups is comfortably far between, so that you can get some story progression in between.
The terrain and different levels are flexible enough for you to choose how to progress and what bosses to fight. The story doesn't suffer from this at all.
The badge system is interesting to say the least.
Then the greatest part, the bullet hell fighting. This is so great. The patterns are unique for every single boss, and there's like 40 in this game. It's like crack for a bullet-hell maniac like myself.
The final boss is something else entirely, I love it so much.
There also is quite a lengthy after-story to this game. 4 bosses, which are way harder than the final boss. After that there's 3 bonus bosses, which are hard as hell.
There's also a boss rush.
Overall, if you like tough-as-nails difficulty, metroidvania platformers, and touhou-esque bullet hell goodness, pick this game up.
I loved it immensely, and it was the much needed breather I needed in between VNs.