It's like fantasty Fallout, but with more freedom, imo. Like, if you do things like join the thieves guild you can just mess around, steal crap, and then you have to sell them to a fence instead of a regular merchant, since honest people won't take your stolen goods.

Main quest is easy to ignore and not nearly as exciting as Fallout 3's, which lends more to you goofing off in the game and doing the badass side quest missions. If you play it, DO THE ASSASSIN GUILD. Trust me. It is deliciously fucked up and you will love it.