Fun little platformer! I'd have liked to see more puzzle elements. Games with world-switching mechanics like this (like Giana Sisters: Twisted Dreams) can do a lot with puzzle elements alongside the platforming difficulty.
The biggest critique (which others have talked about) is the camera is too high relative to the player, and stays fixed on the player.
I highly recommend reading this Gamasutra article on cameras in sidescrollers. Something like the platform-snapping camera-window used in Rayman would do wonders for the issues that your camera has.