Arkham City is, realistically, going to be up the top of a lot of people's Game of the Year lists. The main difference between it and it's predecessor, Arkham Asylum, is the size. Arkham City is… well, it's a city; the new mayor of Gotham has penned up every insane and diabolical criminal within a large section of the city itself, surrounded by towering, fortress-like walls, and policed by a private firm, TYGER. Batman finds himself thrown into Arkham City, as it's known, and from there on in, things get interesting. Dancing around squealing with joy interesting.
Arkham Asylum was revolutionary in that it allowed players to become Batman, and the combat system, gadgets, talent unlocks and stealth innovations made the gameplay feel unprecedentedly authentic. In Arkham City, everything has been supersized; the combat is far more fluid, and the new finishing moves are way more intuitive; in Asylum, you effectively had two kinds of brawling - stealth and brawling. With stealth, you could pick stragglers off one-by-one, luring them into traps, grabbing them from out of the darkness, pulling them into air vents, all the while screaming things like "I'M BATMAN!" or, on occasion, "EAT A BAG OF DICKS, BAD GUY".
In Arkham City, the line is far more blurred, given that most combat takes place in city streets or on rooftops; you might get one or two stealth takedowns off before the rest of the crew you're after cotton on, and flood in on you. This is when you get to deploy all manner of gadgets to help clean things up, and whilst your staples are there (batarangs, batclaw, explosives), you're also gradually fed several new ones, none of which I'll mention here, because frankly half the fun of being Batman is getting to find out what your wonderful toys are.
The voice acting is, as usual, superb. Kevin Conroy once again does Batman (and he really is the best Batman there is), and Mark Hamill returns to bring life to The Joker one last time (he recently announced Arkham City was the last time he'd do The Joker). Another noteworthy voice talent you'll encounter is Stana Katic, also known as Beckett from Castle. I won't give away who she plays, because frankly if I named every character in the game you'd hate me forever.
The main campaign isn't terribly long, but it is varied, frighteningly tense, and beautifully paced. It's also peppered with a fantastic array of side-quests, which you can either head off and finish up, or save until you've completed the central storyline. Also, Arkham City does what no other sandbox game has done; it frames the post-story foreplay mode squarely within the narrative, with Batman declaring that there's a great deal still to be done to fix up the mess made within the narrative. From here (provided you didn't play the game on easy) you can equip any DLC costumes you've unlocked, or even switch at will between Batman and Catwoman.
Incidentally, before I finish up this rambling ode to what will surely be my game of the year, the Catwoman content - simultaneously a fantastic little tie-in and a surefire way to ensure a minimum of game piracy, by providing one code per legitimate game purchase - is a terrific idea. There are four Catwoman chapters that pop up at pivotal points throughout the story. She has her own talents and gadgets, and whilst she's clearly over-sexualised (even mores than she usually is in the comic series), she's an absolute pleasure to play. Also, if you've got the Catwoman bundle installed, there'll be a point in the game where she gets to decide the fate of the entire city. Ballsy stuff.
Honestly, the game is going to be a lot more fulfilling if you're (a) a Batman fan (and by 'fan', I don't mean seeing the movies. I mean someone with a decent to excellent background knowledge of the Batverse, be it the comics, or the alternative reality in which the animated universe resides), and (b) if you've played Asylum. It's riddled (pun intended) with nods to minor characters, easter eggs, fantastically conceived side-quests and, let's face it, nothing can surpass the freedom you feel when you're Batman, and you're zip-lining between buildings to dodge machine gun fire from a pursuing helicopter, or free-falling towards the spine of an unsuspecting goon from twenty stories up.
In short, Get a copy. Now.
...And before I finish up here, if you're after the just-released trailer for the Nightwing DLC—here it is: