Gamespot is low-balling this game. Just do some boxing with some old friends and you'll see why it's at least a 9.25.
You get an awesome upper body workout too.
If you're playing this game alone, yeah, it's going to kind of get pretty old over a bit of time. But hey, if you're with friends, this game will continue to return dividends on the $250 + tax investment you made on the Wii.