Certainly didn't blow me out of the water but you spend an hour on while you rest your "trigger finger"
The thing that I feel is crucial for a game such as Sega Superstar Tennis is a story mode because you need something to draw the player into the game, into spending countless hours on the game, putting it down only because they know they have to wake up in several hours and they need to be able to function. This, is where SST fell short. It contains no form of a story mode, only missions mode that quickly tires the game. Even on tournament mode its the same old same old score activate your power score, win the game and advance.
However overall the tennis playing isn't to bad. The fact that you can activate a kind of "super-mode" brings a difficulty factor to the game. It can either help you out of those tight spots where your down 45-love and you need the game. Or, it could play against you, your opponent activating it when you just wish it was a fair game. However the fact that it only lasts one point there is no real disadvantage/advantage to it.
SST is a mediocre game with mediocre content, neither being out of this world or something you'd never want to consider buying. If you need escape from those hardcore pokemon battles or maybe a console duel, this can definitely consume the time you put away for it. However the fact that it gets dull after some time, its not going to be something you spend those all nighters with your friends on.