I'm honestly not clear on the aim of the game: is there a scoring zone? Is there a way to miss a return and get blown up? How does one gain score, or win, or lose?
(Forgive me if I missed some demonstration of this in the video--I think that I was somewhat tired when I watched it. ^^; )
However, two ideas do come to mind anyway:
1) Different "characters", each with their own traits (speed, return-volley strength, etc.), and perhaps some sort of "special ability" (split the rocket into two for one volley, or teleport, etc.).
2) Various game-modes, each with their own scoring mechanisms; the two possibilities mentioned above might be examples: deathmatch, in which missing a return results in being blown up, and "soccer", in which there's a scoring zone into which one is expected to direct the rocket.
Sorry, it might not be super clear from the video. Basically, those things rotating the players are hearts, and when you get hit then 1 heart goes away.
Soccer actually seems to be a great idea with this kind of game, thanks a lot for that suggestion I'll definitely implement it once I get some time.
I also thought about different characters, but not sure what each one should feature. I'll see.