SEGA Superstars Tennis is a great little game and it doesn't disappoint. Don't expect Virtua Tennis though!
Graphically, the game is nice and shiny though it does suffer from a few framerate issues on the PS2 (none affect gameplay however). The sound effects are all spot on and there are lots of great classic tunes here.
Content wise, there are loads of mini games. Some of them are a bit dull to play through, but there are enough high quality ones to make up for this.
Controls are spot on, though the 4 button system is simplified to 2 button for this iteration. The controls are very similar to Mario Tennis (I believe is the main reason for the simplification) so veterans should feel at home here. The game defaults to an easy difficulty setting, so if you find it a little to easy, make sure to change this in the options. The game still isn't particularly difficult but you have to remember the target audience - young kids.
Overall, Sega Superstars Tennis is a fun little game with lots of content. It might not be as good as Virtua Tennis, but it is easily a game as good as, if not better, than Mario Power Tennis on the Gamecube. If you want realism go for Virtua Tennis, but if you want a fun character based game, then this is a very good choice.