You've managed to make a game that is fun to play, yet challanges your mind at the same time. I like that you have to complete your level before you can actually "create" it, since that prevents jerks from making impossible levels. Another plus is that there is a small variety of items. This mixes the game up, but keeps it from being too complicated. I also like that the stars are not mandatory, but are still apealing to grab.
By the way, check out level 20751.