The acoustic guitar is already awesome. So I wanted to suggest adding more instruments, and also a proper way of playing actual songs. Controlling the pitch by changing the angle is fun to make “noise”, but you can’t really play anything this way. It would be really cool if there would be some sort of HUD or special UI for instruments where one could play specific chords and notes with the keyboard (the num pad for instance).
Just-for-fun features can make this game even more awesome, and I hope my suggestion will be considered!