I love the concept, the art, and the music was very much fitting. It would've been better if the camera speed would match with the player when the player goes just the right amount of distance away from the left side so that the player can still see what's up ahead.
But the fact that each door looks different based on the world behind it kind of defeats the purpose of the theme of wondering "Which world is behind it?", yet a great touch to detail in general.
Aside from that, the game's just great! ^ ^