The game is very nice. Graphics are great as well. I'm playing it in Dx10 and it runs great at 1680x1050 16xAF/Level2 AA option. I like the way you can choose to play the game. Run through the streets picking fights, climb to the rooftops and jump from rooftop to rooftop like a ninja, or sneak by everyone on the streets quietly and assassinate anyone.
The number of NCP's are incredibly high in some scenes. I'm guessing the game becomes very CPU limited when that happens. Luckily, it seems to make good use of Quad core CPU's.
The game has some of the largest playable city scapes I've seen. The towns you get to explore are just insanely large. Especially when viewed from high. I also like the way almost every thing in the game is climbable. Every building, every fence, are parrallax mapped and can be climbed over or on top of. Would be kinda cool if you could also climb the side of mountains though.