Props for these clever puzzles, rising in complexity. I must say I didn't manage to beat the last level (I have a love-hate relationship with puzzles: I love them, but I hate that I'm not actually good at them). Fun game.
The graphics could be a little bit sharper. More importantly, though, a little more feedback (animations, audio, visual effects, GUI elements) is needed to help the player feel their impact on the world. As another reviewer noted, we can't see the player's current weight, which is a really important element.
Audio is one area where a little effort goes a long way--even if it isn't great, it really helps make the game world feel alive.