The gameplay and visuals were astounding. THe story, writing and acting were fantastic: dark yet melodramatic. The controls were buttery smooth. Expansive open-world that revealed more as you progressed.
Short campaign. THe replayability was the most disappointing. The riddler challenge system was upgraded but I found it to be convoluted and difficult to use. Chasing down those stupid trophies only to find little progress made toward unlocking a new riddler hostage challenge. No new batsuit unlocked after playthrough: what's up with that? It would have been nice to be able to change the difficulty setting for the replay+ (i.e., the campaign replay w/ carry over upgrades, progress, etc). It's kind of a 0-sum gain when a fully upgraded Batman takes on more challenging enemies. And it's not like I have an incentive grind through since there's nothing left to upgrade at the next level-up. All I wanted to do was kick some butt with my new toys. See Dead Space 2 for replayability done right.
I am one of the staggering minority of people who did not like Arkham Asylum. I thought it was repetitive and constraining. I hated having to use Detective Vision all the time and thought Batman deserved having a city, not just a bunch of corridors, to walk around.
Well they gave Batman a proper city and Arkham City is a much better game. The combat is pretty much the same but they switch it up with set pieces and different types of encounters. Because you're in the city for most of the game and not in a series of rooms, using Detective Mode to plan out how to take down enemies is more fun this time around.
I finished the main story (playing on normal) in maybe 8 hours, without playing many side missions. I found the side missions frustrating and repetitive, so I didn't bother. What is most disappointing about the main story is the boss fights. There was only one boss fight that I thought was properly difficult. The rest were ridiculously easy.
Rent this game, don't buy it. If you play all the side missions it will only last you maybe 15 hours. Good game, not incredibly memorable though.