I like the bright aesthetic and the fact that the audience will look at the ball (looks cute XD).
The game mechanics is interesting as it primarily rewards reflex rather than accuracy (compared to other sports games).
One critical point I can give: Getting in the circle will freeze the character, but this may render the character unable to hit the tennis (depending on angle). In my opinion, having a way to maneuver inside the circle (after locking in) would be nice.
All in all, a quick and fun sports game.