This looks very polished and nice, and it's an interesting concept, and fun to play. Loved the art and boss design, and the idea of limited attacks that you recharge by doing another thing is cool.
The screen got very busy at times though; e.g. the extra notes that appears when you successfully match instruments just adds to the chaos, which is maybe not what a player wants upon successfully doing something. The particle effects that appear when the instruments swap out is particularly distracting. (Maybe this is intended though?)
I also would have liked to see a better health indicator; I think the lightness of the player is an indication of that, but some clarity on exactly how close you are to dying would have been nice.