Well done, I like the music, it's really catchy. It would be even better if you could add some effects, like particle effects, when I hit the beat; the current feedback is weak.
However, I haven't fully grasped the game yet because I have to keep my attention focused on the bottom left corner to avoid missing any beats. The only thing I'm sure of is that hitting the beat gives me a benefit, but I don't know exactly what.
I saw a very complex results screen; I think you've done a lot of work on that, but I think it would be even better if you could refine the game's feel.