Thanks for all of the feedback!
I lost way more time trying to get the dragging to work than I intended going into it, and certainly could have felt better as the key way you'd be interacting with the game. And it sounds like you hit more bugs along the way.
I was really torn about how much to walk the player through hints and give clues versus letting them discover it, not sure how much people who know the pieces or music theory. I like your idea of the hint so people could have a north star to work towards!