Are you kidding me?
The adventure is short, especially considering the normal length of these things. You'll be done with single player in 8-10 hours, max. The cooperative play is abysmal, absurd, and insulting. If you want to play online, then you get no loot, no experience, no gold, and you don't even get to use your own character . . . unless you're the host. So, why would anyone ever play online? They probably won't. What year is this?
Okay, so it's a passable loot-grab in single player. But so are Torchlight and Deathspank . . . and they are about 1/5th of the price (math?). I couldn't have been more disappointed, especially considering Dungeon Siege's pedigree. Save your money unless you're really, really, hard up for this genre.