My main complaint is that it's hard to tell where to use the instruments. I'd recommend some visual reaction when you play, even if it's the wrong notes.
I kinda get where you're coming from but that runs counter to the philosophy of the game.
- The intended flow of the game is to explore, find something unique, and then try to figure out its significance using the limited options at your disposal. It's about observation and testing theories based on clues, not blindly throwing everything at the wall. So figuring out how to interact is part of the puzzle (and once a pattern is learned it does get reinforced).
- Having an immediate reaction encourages brute forcing, because it would incentivize players to just wander around playing notes randomly until something happens and only then try to figure out what it means.