This is not tennis >:[ and here's why!
Visual
The game has a simple artstyle, but it works incredibly well!
Audio
Great sounds, but maybe it misses something when there is a change in gameplay :)
Tutorials
Unfortunately nothing to tell the player how to move. Would've helped me to see it was a two-players game.
Gameplay
I like the non-necessarily mirrored gameplay between the two players, and the fact that it's not only a graphical change but a gameplay change. The only bad point I can see is that it's the same order for both players.
Fun
I had fun playing against myself, it must be even better with a friend!
Bugs
There is a sound bug when the ball is against the ceiling or the floor, or just if you move with the ball, it will spam the boing sound.
If I'm right, the ball teleports above you if you crush it down while it's going vertically. But that's not really a bug, just weird.
Theme
Yep, it's in the theme :)