I really like the idea! I feel that the audio could be tweaked a bit more, it felt quite dry, maybe mix the sounds more, add more variation to them, a little reverb to count for the environment. Would have loved some SFX for footsteps as well. But I really like the idea of using the sounds as attacks and placing them on the loop, it's pretty neat!
In terms of gameplay, I though that spawning in the room after getting a new instrument was a bit brutal. Maybe having an in between empty room would be nice, so the player can decide to go in the next room :)
The animations are really nice, I like the vibe from the game, it fells rather polished. Great work :)