Really cool concept. I was very impressed by the way the bullets pile up and are usable as a platform, that is a very cool mechanic indeed. I found some of the movement - with regards to wall jumping/climbing - to be a bit janky feeling. Not exactly sure what, but maybe it would benefit from more of an outward velocity when breaking from a wall? Not sure. The art, music and vibe is all very cool as well, and the floaty mechanics when shooting downward was fun to figure out. Jump + kicking is very subtle and I think you need to make it more obvious or add in a separate kick button, I could not tell what was happening as I repeatedly tried to kick the shielded enemy. Also, jump invulnerability is a very odd choice.. makes more sense to have a dash or shield or something (just my personal opinion). Also, I was able to trigger the centipede boss without entering the room, and thus was able to stand in the doorway and shoot it from safety.
Overally, very good work + progress!