I like the hand drawn art style, nice work on the layering. The tiling, particularly on the internal walls feels pretty bad though, and the fall through platforms feel like placeholder art.
I really like the jump shoot mechanic, that feels fun to time and you feel pretty mobile once you get the hang of it. It would be nice to have an indicator for bullet charge.
Feedback on the dash doesn't really make it feel like the kind of thing that would break walls, but since you had one right in front of where you pick up dash it makes sense to try it. Some sound effect or animation on breaking the wall would also be nice.
I almost exited the game before the boss fight since it was unclear what I was supposed to do, I hit e on a whim and it entered the boss fight. Unfortunately the original level music did not stop so I had both it and the boss music playing which was a bit annoying.
The progression is a bit linear but solid little game.