the theme is simple and strong, and having the world be composed of cardboard really drives it home. The Amelie music fits really well too. The graphic quality could be improved a lot though - even though you can tell you used cardboard, the perspective is off, so you don't get the 3D feel that cardboard should give.
Have you heard of a book called Cardboard Universe? It's really cool, about what I think you're aiming at here: how fragile the walls of 'reality' are