The first thing that happened to us upon launching Tennis On-Court was a hard crash. Even before we saw the main menu, we were on the error report screen. The game would only crash a couple more times, but it was a worrying start.
Worse than the crashes is an annoying bug where, if you hit the tennis ball at just the right angle, it'll hit the net and fall beneath the court, but the play won't end, soft-locking the whole match. This problem is so prevalent that around half the tournaments we tried to play had to be abandoned before they could be finished.
To rub extra salt in the wound, the gameplay is really fun. Hit detection and tracking of both the ball and your racket are exceptional, aiding in the whole experience. The handful of courts you can use are also nicely rendered, offering different colour schemes as well as surface types. As you play, you'll notice how differently the ball moves based on the surface — turf vs. clay, say — and be able to account for that. The AI is quite capable of keeping up with you too, matching the velocities and tempos you adopt. It makes achieving a flow state during a volley quite magical.
Presentationally, while the courts do look nice, character models look downright demonic. They rarely emote, and when they do, it is disconcerting to the extreme. Even just adding an animation for blinking would help a bit. The crowd is lacking as well. The stands are packed with sprites, but they barely move or react to anything at all, and they only make noise in between points. Sure, it's good to respect the players out on the court, but during volleys, things can get eerily silent.
That describes the game on the whole, really. A give and take where one element of the game is great fun, but another is broken or unpolished. What you're left with is a game with a super fun core that's unfortunately too broken to put any meaningful amount of time into.