Well, I have this game since it came out and used to hate it, until last week when I decided to give it a go and try to complete all the achievements.
When I finally learned how to play on hardcore with Katarina and stopped having my ass kicked at every fight I started to really like the game. Now I'm halfway through it and I'm really enjoying the experience.
Now, comparing this with the other Dungeon Siege games, Diablo, Titan Quest and all other games like this out there... well, everything else is still better I think.
But if you can get it cheap and really like dungeon crawlers like me you will enjoy the game. Just don't count on people online to play with, everyday when I launch the game I check how many people are online playing, I would say you can usually find 5 to 10 people online at the same time.
To make things short, get it when you don't have anything else to play. 17 days away from Diablo III is not the best time to start Dungeon Siege III, that was my mistake when I got the game, I had A LOT of other good games to play and it ended up lost in my room until last week.