Awesome little game. I liked your interpretation of the theme and the art direction.
The progression in mechanics and difficulty felt very good and the 3D section was a really cool surprise. In the 3D sections the mouse started drifting. I'm just reporting this as a bug, I don't consider it a failure because is a problem I see in a lot of Unity web games and also because the 3D sections are so short that it isn't too annoying.
I liked the implication that the hand at the end of the first phase is MMN's, as it appears when you beat their highscore. Makes me think that there is a deeper lore there.