Well, the AI is meh, at most. It's very cool to see so many people roaming each city but the real problem with AI is the combat. You can actually see it in the videos of the game as well. You can battle several guys at once, which is neat, but for some reason only one of them will attack you at a time, adding a slow pace, at that. It's definitely worth checking out but not buying, for me at least.
My favorite new releases, at the moment, are Call of Duty 4 and Mass Effect. Mass Effect is probably the best single player game I've played in the past year or so.