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.