Thanks for the review!
> You can actually always press all 4 Buttons at the same time since there's no penalty to hitting notes when you shouldn't.
Rhythm games either decide to punish "ghosttapping" (tapping without notes present) or they don't. I chose to go with the latter to make it easier for beginners with a hitmiss window of 100ms (lower = easier), however it's true that the notes on easier difficulties are spaced apart too much to get punished. It would require the hitmiss window to be at least 600ms at the beginning of easy difficulty (1min/25bpm/4 notes per measure = 600ms per note), at which point I could simply punish ghosttapping altogether which, to be fair, is more accurate when comparing to actual piano playing.