Combat has been mostly unchanged from the original game. There are some new moves and gadgets, but it flows exactly the same way. It was pretty much perfect in Arkham Asylum so not changing a whole lot makes perfect sense. What they did though, was hone it to near perfection. Boiled down to it's basics it is still punch, punch, punch, counter, counter, punch and you can win just about every fight like that. It's when you mix in Batman's utility belt of gadgets that it really gets spiced up. Leaving small amounts of explosive gel on the ground while flipping then blowing it up and stunning a group of enemies, or whipping a bad guy in the face with a batarang in the middle of a combo, or tossing an ice grenade at someone and freezing them, or whatever your imagination desires...it's all possible and it's all awesome. This is how Batman fights, with his wits as much as with his brawn and skill. Racking up a wicked high combo feels awesome(so I've been told, I max out around 25 hits or so).
The biggest change from Asylum to City has to be the actual map. Arkham Asylum was a small map located on an island outside of Gotham. There were a handful of buildings, some caves and tunnels, and that was it. You ended up revisiting the same areas a lot and the variety wasn't all that great. Arkham City on the other hand, is a living, breathing piece of metropolis. It's gritty and dark and beautiful. Everything is perfectly detailed, there is no wasted space at all. I'm not sure how much bigger the map is then in Asylum but it is at least 3 times as big, and swinging and gliding around all of it is breathtaking to say the least. There are now goons everywhere to fight, sidequests to solve around every corner, hidden riddler trophies are all over the place(and a lot more cleverly hidden), and enough other side content to keep you busy for weeks.
I'm not going to say the game is perfect so that means I have to complain about something. Some of the boss fights are a little uninspired or just don't plain happen like you think they will. There a few situations where you are expecting a kick ass fight aaaaannnnnnd...nothing happens. It's a little disappointing. Also, there is a game mechanic in particular that I found annoying. There are multiple parts where you have to make a little ice shelf to stand on and then pull yourself around with the grappling hook. It's tedious and they use it quite a bit. These are really minor complaints and I normally wouldn't even mention them, but I feel obligated to say something negative if I'm going to say a game isn't flawless so there you go.
The story is solid, there are some nice twists and surprises (FUCK YOU KOTAKU) and it is paced well. The side missions pop up during play so if you do them as you go it can easily take 20+ hours to finish the game. If you go searching for every riddler trophy, you're looking at around 40 probably. I was into the story quite a bit so I skipped a lot of the side stuff along the way and I finished it in probably 10...maybe 12. It never gets boring, though if you install the Catwoman stuff it gets interspersed into the gameplay. You play as her first, then another mission soon after, then you get nothing but Batman until near the end and BAM! they throw another Catwoman part at you. I hated how they mixed it in at the end, I was into being Batman and they completely interrupted me. Playing as Catwoman is interesting. She is a hell of a lot faster than Batman and can cling to chain link ceilings and her cleavage is always out and she does sexy slides that don't seem to be the most functional but overall her parts feel unnecessary. I kind of wish they hadn't bothered mixing it in, or at least given her a bigger role and fleshed (OH HO HO) her out a little more.
What can I say, it's Batman. They did manage what I thought was impossible and made a game that met or exceeded everyone's expectations. It's the closes thing most of us (present company excluded) will ever get to being Batman. Now that it's done, I'm left frothing at the mouth for more like a rabid, starved wolverine in a butcher shop full of delicious smoked meats. I've still got a fair amount of game left to play too. It will be a while before I'm done with the sheer joy of just plain being THE BATMAN.
