The mini games and tennis rounds are fun until they become kind of old after a while. There is really not a ton to this game but it's great fun. The difficulty curve is a bit confusing as it is easy for the first half of the game then it becomes "stupid hard" as you get to the near middle. It's worth the rent.
With Sega Superstars Tennis, Sega offers us a below average title, and most of the game can be completed within one seating, minus the borderline impossible missions. Don't get me wrong, it is a fun little game, but there could have been more done with it. The 'Superstar' mode of the game takes you through tennis court missions that take place within one of Sega's games. After playing for a little, you realize that, wow, Sega really hasn't made anything worthwhile since Sonic the Hedgehog. Not only that, but the characters are horrible. I only knew who 6 of the 16 (yes, only 16!) characters were, and 5 of those were out of Sonic the Hedgehog. And not only did they leave out the best character from that series, but instead of adding old greats such as Toe Jam and/or Earl, or Kid Chameleon, etc, they decided to throw in a bunch of ridiculous looking characters that no one knows.
In addition, some of the missions are infuriating. The Jet Set Radio stage in my opinion is the worst part of any game ever. While a few missions throughout the game are fun and give the whole 'constantly playing tennis' thing a rest because they are new interesting little challenges, they quickly lose their luster as you will spend mission after mission after mission doing the same thing over and over with little variation.
All in all, it's a game that can provide entertainment, however little entertainment that may be. Playing with a friend is always fun, but besides that, you'll be finished playing this game within a couple days. So if you're looking for some easy achievement points and a little amusement for a day or two, by all means, give it a shot. Otherwise, I can't possibly recommend this game.