Really good and an awesome idea. I
The levels definitely need to be reshuffled or something. I feel like there were 2 very hard ones in the middle and some cakewalks at the end, giving me a very jagged sense of challenge. Visual change up would be nice and maybe more flair. Maybe have levels with similar focused-on mechanics be bundled together in "worlds" or something, each would having its own music. I love that one with the drumbeat and piano.
Feels like a LOT more can be done with this concept with plenty of room to experiment!