You say it's incomplete, so I'm not sure how to rate/review this. The only thing in particular I noticed is that the tennis ball's physics behave very odd. It wiggles around and hovers above the floor most of the time, but after hitting an obstacle it might suddenly go skywards and behaves more like what I'd expect from a tennis ball. IMO it would be more fun if the balls would fly ballistically and the initial angle would be determined by your vertical looking angle.