Extremely polished, with lots of nice little touches.  Good music.  Really felt like a Gameboy game.  Controls were a little slippery, and pushing an object downward moved *way* too fast compared to the other directions.  The game could probably use a "reset room" puzzle.  It wasn't always clear what the keys did when you picked them up.  (Maybe color-code the doors they open?)

All in all, though, good job.  A solid game that I really liked.

An interesting puzzle concept with enjoyable gameplay.
The soft visuals and great sound design made the game really pleasant to play.