cool game, especially the last level is very enjoyable to play.
As for the difficulty, consider giving more information for the moving sprites (like the exploding rects or the sinewave). You could for example draw a grey line half a beat early where the rects are going to shoot, or render an additional sinewave in grey half a beat earlier so you can evade the whiplash in level 3 and not just tuck yourself into a corner and pray ;D