Great single player game, horrible co-op, lame story.
Pros: Highly detailed, family scripts, dog scripts, ability to own everything in sight, fighting, not having to worry about mana, ability to shape the world depending upon how you act, being able to have your character wear what you want without having a armor cost.
Con: Co-op painfully share the same camera, lame story, short story, money system is easy to over-come, easy to max our your character in no time, very annoying to use potions which grant experience, the 'free-roam' word they keep throwing around is not entirely true - you will be forced down road-ways and paths 90% of your gameplay.