Decent Intro to Series
I suppose I am lucky that I didn't play the original two, but I was in the mood for a hack and slash loot fest, so Dungeon Siege III looked like a good option.
And it is not a bad game. It's a bit short (10 hours and I apparently missed one sidequest) but it does hack and slash well enough. It certainly isn't Diablo, but it is probably the best example of this genre I've played on a console, including Torchlight.
I played the game as Lucas, who is basically the tank character of this game. No real range attacks but with more than a bit of resilience. And the game was perfectly playable.
But, that isn't exactly high praise. It's not a terrible game at all --- but there is little really impressive about it. The visuals are pretty decent but nothing to write home about. The enemy AI isn't all that great, more along the lines of just "damage sponges with some nifty attacks". It is, for wont of a better term, the traditional Obsidian game. A perfectly competent, well-made game that lacks the special something to take it from the realm of being a good game to a great game.
Now, I will also admit I played it on single player. I did not try the co-op mode. How much enjoyment this brings to the table is a question...but the game is still extremely simple and not terribly long. I don't see how much this can be helped.
I'm not saying the game is bad. It isn't. It is perfectly fun little game. It just won't blow your mind. Come in with expectations suitably set and you'll be fine.