I agree with Stickle about being able to hold down the movement keys. That would make everything much more smooth.
Besides that, I really loved the colored pencil art style for the background and title/menu, but it did clash just a little with the game sprites. The music was great with some very tasteful dissonance.
The actual puzzle mechanic was straight-forward, but I liked the level design utilizing it. Some of the levels really made me think.