Yeah... Saying Rise of Ballos is "an acquired taste" is a pretty big understatement.
It's hard, and not in a good way, as in, the guy who made it can barely play it, hard.
The difficulty mainly comes from it being unfair beyond belief.
...Really, the only redeeming factor is all the crazy ASM stuff, but imo, it's not worth it.
If you want something that's a bit more well rounded design wise, I'd suggest these 5:
1.
Lunar Shadow. It's a metroidvainia made in Cave Story. Not "quite" finished, but it's really only missing out on some extra end game content.
2.
Cave Story Redesign. It's Cave Story, but expanded into a VERY large metroidvainia, bigger than Lunar Shadow. Fair warning, It's massive size can make it kind of a chore, and it's not complete (ends at outer wall iirc), but still worth a look.
3.
Jenn's Journey. A mod that's only real flaw is the fact that it ends.
4.
Rave Story. It's a meme, but it's also a really good mod.
5.
The Traveler. A "post best ending mod" with a lot of charm! Not a whole lot of actual game, but it's a fun time none the less.