I actually like the idea of a rythm game with the mouse and fast movement ! I would have tried locking the mouse horizontally or make it an in-game cursor (OSs cursors are a bit small for this case) but really it's good :) Oh also the A rating can't be seen on the bottom lane and B on the middle and top lane, but with the 4 colors limitation I can't see a solution except making an outline of a second color, which makes sprites bigger so not taking that into account, just pointing it out !