I'm impressed how alive the world feels. It reminds me a lot of Gothic. Even the NPC conversations are great and make sense, it's a far cry from the terrible Radiant AI from Oblivion.
Even gameplay can be pretty brutal if you step in the wrong place.
It's almost a shame this game is so good, since Arkham City is coming out this week and I hear that is also a brilliant game. Not to mention, Saints Row 3.