Decent game. The concept is simple and relaxing, but most levels are too easy. Only five or so actually require you to figure out a partial ordering. What might be interesting would be a system that allowed the player to draw over the map and "mark off" areas that need to happen in order. In this way the game could be harder but the player would be given the tools to keep up with the difficulty increase.
Logging the number of moves used to complete a level (and rewarding players for doing it in fewer moves) would also be super nice.