If you have friends, buy this game. Otherwise, only purchase it if you're a hardcore fan of the series.
Gameplay:
The game revolved around traveling to different regions inhabited by enemies which you must defeat in order to reach the "myhrr" (or whatever) trees. Drops of water from these trees are necessary for keeping civilized towns alive with oxygen. Without myhrr (or whatever), then the toxic air which surrounds the towns will kill the civilians. The high point is playing with your friends and fighting these enemies together.
Graphics:
Nothing very special, especially when compared to the GameCube's possibilities.
Sound:
There's no voice acting, and the sound effects themselves are particularly noticeable. On a sadder note, the music can be sometimes annoying.
Value:
This is where the game specialized. The game itself seems never-ending, and playing with friends can offer countless hours of fun. However, this is where the value ends, as without friends, the game is next to worthless after a while.
In the end, this game is intended for the sole purpose of great multiplayer. Only the hardcore fans of the series will enjoy playing this game solo for long amounts of time.