I've never played Sega Superstars on the PS2, But I owned somewhat of a sequel? Sega Superstars Tennis, a bunch of Sega/ Sonic team mascots ripping off Mario Tennis but doing its own thing. Sega Superstars Tennis has a lot of content like the Superstars mode: a mode where you unlock stuff from different genera's and missions, Match mode: where you can just play or practice playing Tennis with CPU or Multiplayer, Tournament mode: just like it sounds a Tournament playing 4 matches to the final either Single or Multiplayer, Games mode: an arcade of Classic Sega endless time games either Single or Multiplayer, Online mode: where you can play with people from around the world (but it doesn't work for me because I couldn't find anyone to play with), and options mode: where you can view states or change settings. Their are also characters and courses to unlock in the Superstar mode. So the gameplay itself, it's just Sega characters playing Tennis, you control the characters with the left stick and hit and shoot the Tennis ball with X or Square. But when you serve the ball, their is a meter on the side that the strength of shooting the ball can be charged, the meter jumps and if you time it just right with full stars then the meter maxes out to unleashed a more powerful shot making your opponent lose balance. Characters also have their own "special abilities" called Superstars, their is a star below you with a yellow outline and the more you win a point or keep hitting the ball, it builds up and gets filled with yellow, when it gets full then you can unleash your Superstar mode, if your struggling to get a hold of the tennis ball you can use this mode to help you get back on track with an extra boost of speed, distracting your opponent, or making him/her disappear to lose track of the ball.
Sega Superstars Tennis is not a very memorable game, it just sort of exists. But it's a decent reception, and it wouldn't hurt to buy it.