This game is great! I really like your interpretation of the "feedback loop" theme, it's quite clever. As someone who really enjoys rhythm games, I think it would've been really satisfying to somehow have the notes automatically fit a BPM when you first write them in...or even simpler to add a metronome ticking sound at variable Tempos. I think this would help especially since you're writing a "song" in the game's context.
Personally, my favorite is probably the people dancing in the back. Overall, I really like the idea for this one and the option to bind your keys at the beginning is very convenient.