Played it for a few minutes.... this game actually has potential.
If you can figure out how to label the Notes (C, A, A#, B, etc) and flash the notes as they play in the replay, I genuinely think this can be a super awesome learning tool for learning music theory and ear training.
Tons of other things you could add too. Like a "Chords" mode, where you collect keys in a certain scale and then it plays a chord in addition to a melody. Or instead of simple sine waves, having actual instruments (like a piano, etc) play.