Cool game ! I think the metroidvania was really cool.
I think the movement is really uneven, the movement speed is really fast, while the jump is very slow, meaning I would often bump into corners from moving so fast while jumping so slowly. Same goes for the attack, the attack is really short range for the movement speed you get, so I would often struggle to get in range of the melee attack without hurting myself on the enemies, specially the big redblocks that moves as much as fast as you.
I think there's a lot of issues with signaling and feedback, a lot of things have the same art while not being the same, all enemies are a red block, but those on the ground could be either destroyed in one hit or explode after getting hit and there's no way to know unless you already know, checkpoints took me a while to understand were checkpoints and the health upgrade look the same but is not a checkpoint.
As for level design, since everything looks yellow, it's often hard to tell where you are therefore hard to tell where to go. Some spaces look like you would fit under the damage zone but you get hit by like a single pixel and get hurt, kind of feels like a cheap shot.
The upgrades were cool, I got the wall jump and the double jump and the first one about getting stronger when you get hit ? That one I didnt really understand, it's like the first thing you get and I just bumped into enemies to get stronger and died, not sure what was the effect of that one.
I gave up after wandering for a while after getting the double jump and didnt know where to go and the difficulty was kind of brutal and the jump controls were not responsive enough so it felt frustrating dying again and again on the damage zones.
I think the base of the game is cool, the level design is cool, if the controls were a bit better the difficulty would be ok. I think a good improvement would be with signaling and feedback, a lot of thing are not properly explained or easy to understand.
Sorry for the wall of criticism, I'm trying to help with constructive feedback. You have a nice game here with a lot of potential.