Great game, addicting puzzles and creative premise. Some nitpicks, though:
-Slippery physics make some sections frustrating, especially when on a background, or maybe i'm just bad.
-Animation when getting out of a background keeps you invisible for a sec.
-Since esc is the key for pausing, it doesn't work on full screen, it just shrinks the screen.
-Some background sprites aren't aligned to the pixel grid, but that's more of an opinion on my part.
These are really small things, and don't really hamper my enjoyment of the game. (except for the slippery thing)