I've been meaning to play this one for a while because it looks very flashy, and now I finally got to it! I think it's good, but it has some shortcomings.
Visually, I think this game excels. You make striking use of the three colors you decided to limit yourself to, and you clearly know how to utilize particles, screenshake and other effects to make objects, characters and actions feel lively.
I don't like the respawn system. I'd rather explore the rest of the world than be locked in a boss arena that I have to knock my head against over and over. I found the appearance of the final boss to be very sudden and unexpected, and I think I missed at least one room with a breakable wall because I wasn't able to leave the boss fight. Now, unfortunately, aside from that one occurrence, making the player respawn outside of the boss arenas would not have actually changed anything, because there is very little to explore in this game, it's pretty linear. I probably missed something because I couldn't figure out the piano puzzle, but I can't imagine that it leads to something consequential.
I found the music to sound interesting in the beginning, having a sort of dreamy feel to it, but that faded after a few minutes of hearing the same loop over and over again, at which point I did find it at least a little annoying, though not unpleasantly so. In my opinion, the boss fight music didn't particularly add any tension (if I remember correctly, one fight didn't even bother with music and just kept playing the same basic loop).
In general, I found this one to be somewhat lacking in the Metroidvania department. I don't think there was ever really more than one way to go (that way being a path to the next boss fight or upgrade), so the feeling of exploration that I deem somewhat important for Metroidvanias was more or less absent.
Sound design is pretty good, very crunchy.
This is more of a subjective take but I didn't like the combat very much, which is unfortunate because this game seems to be trying to be about combat more than it is trying to be a Metroidvania (I am judging by the amount of arenas and boss fights). For the final boss I did end up resorting to just standing in a corner and timing my parries, I imagine if I did anything more complicated than that I would've just died sooner or later.
Jumping didn't feel great to me, the process of rising up to max jump height is veeeery slow. Nevermind's review already addressed why this is and how it can be done better.
Due to the boss designs and the somewhat cryptic NPCs, I'm guessing you had some kind of story planned, though it doesn't really come through in the game. The ending was pretty abrupt and sort of anticlimactic.
It feels to me like you were planning to make a combat-oriented boss-rush esque game from the beginning, adding the whole Metroidvania world aspect of it as more of a secondary restriction. In terms of looks this game is one of my favorite ones from the jam, the gameplay is good on paper though not my personal favorite and missing part of what I like about Metroidvanias. Still, an entry with this level of polish is a very impressive feat that deserves recognition!