Very fun
As others have said, the tutorial needs some work, but it only took me a couple minutes to get it down. The edges are incredibly annoying, but not necessarily in a bad way. Possibly instead of damaging you it bounces you with ~1.5* the power of a kick? Or maybe a blue powerup that does that for you?
The powerups are cool, but the one that adds cymbals hurts to look at. Possibly tone it down or make it an outline?
Music is good! Adding more instruments might be interesting, but only in later levels.
Probably add more levels...
A ranged enemy that fires a slow moving bullet?
The bullet might be destroyable w/ laser?
Other than that great game!
Hope this was helpful!
- Knee Remover/Thief/Destroyer