Phenomenal level design! I felt so satisfied having gotten the key and opened the chest.. this game's puzzle truly uses the door as a mechanic very effectively, and makes you think laterally. I can imagine, it would be very hard to make more "worlds", but honestly, I would totally play a game with this kind of thinking... Very well done, and needless to say, the art, the music and the visual effects were just perfectly suiting it.
Please do try out puzzle game too, and let us know how you felt! :D