I am really digging your game concept! It was very fun to play and it is a nice game mechanic. It is also pretty cool that you have got different levels. I think an intro (level) would have helped, because the controls were a bit hard to understand at first, but you get used to it. One thing that I noticed was that you could get soft stuck if you and the opponent both have only one direction key left and the ball keeps moving along the same axis.
Overall one of the most enjoyable games that I have tested so far, good job!