Never confuse motion with action
Let's really look at what this game is: it's an intensely fun multiplayer game with limited levels, limited options, but very solid play and game mechanics. It's a fun game, and can be incredibly addictive. It's also US$40, which seems like quite the price tag for such a slight game.
Despite all that, I really think Rockstar missed the boat here. If they had made this a Live Arcade game and sold it for US$20 it would have been damn near a perfect 10. With this price tag and the amount of features you get, the scoring is much harder. It has a lot of polish and it's clear a ton of love went into it, but it's a very narrow experience. Once you have played for ten minutes, you have seen almost everything the game has to offer.
He's going to cry himself to sleep on his giant pillow
It's a good game, but it would have benefited greatly from a create-a-character mode or a career mode, or anything to expand the single-player game from simply practice for online matches. Will climbing the Live leader boards and the love of competition be enough to keep you playing the long term? If so, this is definitely the game for you. For everyone else, this is the perfect weekend rental.
It may just be that ball being hit back and forth, but it's incredibly refreshing to see a company do one very simple game incredibly well rather than make an incredibly complex game that simply paints over old numbers. Rockstar is showing some class with this title.
The Good:
Solid graphics and framerate
$40 price tag is less than most Xbox 360 games
Intense online play
The Bad:
There's simply not a lot here
$40 price tag is not quite low enough for what you get
Limited offline play
Unlockables can be tiresome
The Ugly:
Lui Ping's giant, scary head