Absolutely loving the game. I'm only a couple hours in, but thus far, it's my dream open world game. In recent years I've grown rather tired of "sandbox games" as I feel they sacrifice quality level design for the sake of a large world. Arkham City, however, offers a perfect blend of a large, open environment and expertly designed mission areas. You never get the feeling that detail or complexity were sacrificed for the open world.
I also applaud the lack of a mini-map with mission icons pasted across it. The average sandbox game these days devolves into following a series of icon on a map and triggering an event or mission upon reaching it. Batman actually pushes players to explore the world and become mindful of the environment. You're not simply chasing icons around a map.
Once you step into the proper misisons (which transition smoothly from the world map) the game delivers the kind of action you expect from Rocksteady without missing a beat. Great stealth, addictive combat, and loads of variety are all within.
I'm rather impressed that this was all achieved with Unreal Engine 3. Not only is the world map absolutely massive in size, but the loading times between new areas are also incredibly short. Furthermore, playing on PS3, I'm shocked that the framerate is generally so consistent. Some tearing pops up once in a while, but overall, the game runs very smoothly despite pushing the engine to its limits. Anyone notice the bokeh depth of field used while using the first person viewpoint? First time I've seen this used in a UE3 game.
Can't wait to spend some more time playing it later today.