Could use a bit better hit detection. Especially since I find I have to rush to save the ball almost all the time, it's frustrating when it gets stuck inside my paddle.
Add bounds-checking to insure the ball and bats do not travel beyond the boundaries of the playing area. Also, doing a simple sign-change on the vertical velocity of the ball when it strikes a bat is not sufficient. You need to deal with the ball striking the edge of the bat (especially with bats this thick)