Here are a bunch of details, courtesy of those bastards over at NeoGaf:  

 Sharp took credit for getting the Joker situation of the first game under control. He then used that incident to help win the Mayoral election. After winning, he declares Blackgate and Arkham unfit, and buys off a portion of the slums of Gotham. Walling off the area and calling it "Arkham City", he contracts a mercenary group called Tyger into defending the walls. The prisoners are only given one rule: "Don't try to escape", with the penalty for doing so being death. Beyond that, they can do whatever they want within.

-Hugo Strange heads the new Arkham, though it seems like this fact is cloaked in mystery to the outside world. Those who look into him disappear.

-It's been a year. Two face is admitted into Arkham City and he realizes he has to make a move to assert himself in the new prison lest he be eaten alive (not literally, of course). He captures Catwoman, figuring a public execution should do the trick.

-The team is aiming for a highly detailed city, on the level of what they did in the first game with Arkham itself.

-Gadgets can now be used during fights- the article mentions Batman putting explosive gel on the back of one of his opponents during a brawl.

-You can now pull off multiple counterattacks at the same time.

-Many of the super villains have formed gangs, and taken control of differnt portions of the city.

-The team wants to push the "forensics" angle of the first game more, incorporating puzzles in them that will become more complex as the game goes on.

-Most of the key gadgets that were unlocked late in the first game are available by default (Beyond the explosive gel, the article also mentions the line launcher).

-Interrogations replace the Riddler maps of the first game.

-Batman can now taunt his enemies via a button press.

-Certain characters have optional sidestories within Arkham city (the article mentions Zsasz), that you can dig into.

-Harley has a new costume. From the article: "Instead of a nurse outfit, Harley now wears red and black pants, and a matching midriff-baring top. Her face paint has been scaled back to a much more subtle degree, and she now has a Joker tatoo on one of her hips peeking out over her waistband."

-Batman's been given a new gadget called the "broadcast analyzer". The article mentions several broadcasts Bats can listen in on, like the GCPD dispatch and Gotham FM. The main usage here has Batman tuning in to listen to a message left for him by the Joker.

-Oracle is missing, so Alfred is the one in Bruce's ear (at least at the beginning of the game).

-Rocksteady wouldn't detail their multiplayer plans.  

 
 And here is a picture from the game:  

Any word on a release date?

Take a look here. already posted.

 Batman can now taunt his enemies via a button press.  

" Take a look here. already posted. "

" Take a look here. already posted. "

So it's Grand Theft Auto except all the citizens are criminals...
 
Now I don't need to feel guilty going on a crime (busting) spree!

"-Batman can now taunt his enemies via a button press."

I hope there plans for multi-player is none.

Ive got a feeling that Catwoman would be a playable charecter, maybe a co-op mode?

ROCKSTEADY IF YOU FUCKING PUT MULTIPLAYER INTO BATMAN I SWEAR TO GOD! 

Thanks for the find. Best bet would be a co-op campaign with Catwoman for multiplayer as the cover hints at a love-hate relationship and the game will start out saving Catwoman (I think).

 "-Gadgets can now be used during fights- the article mentions Batman putting explosive gel on the back of one of his opponents during a brawl."
 
I'm usually against preordering, but... HERE'S MY MONEY!

" Take a look here. already posted. "

Co-Op with Catwoman. A man can dream.

So... freaking... excited...

I hope there will be a larger variety of suits that we can choose from, but you know, if we are even given a choice.

o god multiplayer. I think i need new pants.

"

 Batman can now taunt his enemies via a button press.  

That doesn't sound very Batman-like.  "

" @kingofpeanuts said:

" Take a look here. already posted. "

If you look at the time of creation for the thread, I beat you to it by a few seconds. "

" I hope there plans for multi-player is none. "

That sounds... kind of crazy, but okay. I'll bite.

I really, really, really, really, really, really, really, really, really don't want to see any sort of multiplayer or co-op in this game. Screw that. I want a nice, long, polished single player campaign.
 
They showed a new enemy who is wearing like... a clown thing and looks like the Jack in the Box guy. He's harder to beat and is larger than the other guys.

There's also a new Gears of War reload-like mechanic to bring down enemies you sneak up on. There will be weak walls that you can crash through to attack people and surprise them. Also, you can summon bats to distract people.
 
By the way, the taunting scares off enemies that are nervous so it does serve a purpose.

" -Batman can now taunt his enemies via a button press. "

" "-Batman can now taunt his enemies via a button press."

"

I am really, really pumped for this. Arkham Asylum is REALLY close to being my favourite game of all time and I have no doubt this game is going to be absolutely incredible.

I really want to hear some details about the stealth in it

Arkham City sounds like it'll be just as good if not better than Arkham Asylum.

Good luck, have Batman.
 
 
 
 
Yes, yes I will. Day one purchase for me.

"

"

" @FluxWaveZ said:

"

 Batman can now taunt his enemies via a button press.  

That doesn't sound very Batman-like.  "

yeah that sounds very wrong, wisecracks during a fight seems like a Robin thing. "

Please.. please.. no multiplayer.
 
If there's one thing I don't want it's mp.

" @damswedon said:

" @FluxWaveZ said:

"

 Batman can now taunt his enemies via a button press.  

That doesn't sound very Batman-like.  "

yeah that sounds very wrong, wisecracks during a fight seems like a Robin thing. "

I'd be fine if the only taunt he says is "I am the GODDAMN Batman".. I would die happy. "