I agree with the previous commenters. The idea is great and you obviously know what you're doing seeing the level of polish the game already has - but I think it's to difficult right now. Maybe try making the platforms a bit wider and stretch them out a little further. For me the game was basically over once I wasn't on the highest note, because then my jumps mostly would collide with the edges of the next note, since the spacing was so tight. And maybe implement a life/health system. I was really proud of getting into the groove, but once the enemies started spawning I had no chance anymore :D
All in all super cool idea - I think if you tweak a little bit here and there this could be really great :)