The artstyle looks really nice, and it's quite fun, but after a while it gets boring. One notable thing is that this uses the limitation to the maximum, which is really nice. Too bad that there's no audio ;(
Another recommandation would be to make two different sprites to the characters, so you can distinguish them a little bit better (in reality, I don't think that will really do, because in the end, if you play alone, you will still mix them up :p ), and that could also help in developing a plot for the game.