This already feels like a quite well-made demo. My suggestions/feedback:
- make it harder to double-hit a drum (usually seems to be from bringing the stick back up)
- make drum hits not register at all when not even close to beatmap notes (say > 0.3 seconds away from any notes hitting said drum) this would make it feel less punishing to players hitting to-the-beat outside of the specific beatmap notes
- a slider for drum size (so you can have larger drums)
- a slider for drum spread (depending on player they might want to be almost surrounded 180 degrees)
- non-drum modes? (like punching)
also, have you experimented with notes appearing in a perspective distance and ending on the tops of the drums which you're meant to hit directly? I feel like this might be a nice option.