The mechanics are super fluid, and it's a nice game that has a very addictive flow state. Absolutely a blast to play, and has an original premise. The controls were super simple and easy to get used to. The experience utilizes the simple premise of a tennis-like gameplay, but is perfectly expressed as a game jam submission because of the polish it possesses.
My only critique is for the greed indicator to be more refined. I was able to return the ball back relatively early, without much of a downside. Perhaps the projectile could lose momentum if it's hit too early. Other than that, this is a very polished game, and that's why I think it's great.
I could see this being a feature in a larger game, either as a microgame, minigame, or training mode. Wonderful job, and I hope this is expanded on in the future in some capacity.