Absolutely stellar work! Really really enjoyed how the game just flowed!
The most minor of nitpicks I have are: The first levels it felt almost too slow to get back to where I needed the track to be if I messed something up.
Putting one false note and having to redo everything did not always feel great. Maybe an undo last note would be nice without trivializing it completely?
Maybe there would be a better character sprite than something that either reminds me of a bullet or of a condom. 😅
Being able to walk on notes while they are being placed trivialized a few parts. Maybe they should just become solid after they are really placed and you can ensure that they are "legal"?
Oh and maybe another keylayout? maybe something like 1-4 and q-t. 1-8 felt a little stretched at times and I often missed the key I actually intended. You could maybe make the number keys treble clef and the letter keys bass?
The deafening effect while in the no music zone is super stunning I love all the care you put into it. Hearing a song you yourself wrote at the end of each track is really amazing!