A decent game, but more flash than substance.
The graphics are excellent, and the characters and plot are well-written and voiced. So from a audio/visual standpoint the game really did a very good job; and was quite enjoyable.
The combat system from Arkham Asylum has returned, which is mostly a good thing, as that was a well designed combat system and worked well for the game. The only complaint that I have with the combat system is that it would have been more enjoyable if the enemies stayed down for slightly longer after being knocked off their feet; I say that primarily because the combat system allows for a lot of variety in moves and the way you can string combos together, however rarely do you have enough time to be creative like that. More often than not, the combat is too long, hectic, and has too many simultaneous opponents to enjoy employing any real finesse; instead devolving into either button-mashing or finding 1-2 combos that you can easily execute without thinking about it. The combat though was still enjoyable, despite the shortcoming.
The biggest problems that I had with the game were the main story being far too short; and the tedious over-emphasis on what basically amounts to "mini-games".
The main story was quite enjoyable, and I liked the way that they writers/developers managed to integrate multiple villains into the game. It was nice to see some of the more "rare" (from a video game standpoint) villains in the game. Tons of Batman games include the Joker, or the Penguin; but few include characters like Clayface, or Solomon Grundy. So I enjoyed the diversity of opponents.
The story though did suffer a bit from the diversity in that the game had a very schizophrenic feel to it, jumping all over the place plot-wise and lacking the depth that Arkham Asylum felt like it had. I really enjoyed Asylum, a lot; so I had a level of expectation for Arkham City, that unfortunately it did not meet. Don't get me wrong, Arkham City was "decent", just not "exceptional".
The game would have been much better if the developers had spent more time on the actual main story concept and less time with their little diversionary mini-games (such as the Riddler Trophy's & Augmented Reality Training) segments.
I found the Riddler Trophy collection to be just annoying and tedious. I spent time collecting about 50% of the Trophy's but eventually succumbed to the sheer boredom of it, and stopped...I just couldn't take any more of the drudgery of the activity.
The Riddler Challenge Rooms (to rescue hostages) were very enjoyable however. I would have rather done more things like that, regarding the Ridder in the game, rather than the stupid & tedious trophy collecting.
I believe the game would have been far better served if the developers had spent far less time on Ridder Trophy's and instead used that time to actually further the story of the game.
Similarly, the Augmented Reality (AR) training was useless. It's worth doing the first set of training just so you get the Grapple Gun upgrade; but sadly the AR training was nothing more than a flying mini-game, and a poor one at that (finicky controls, little to no margin for error, tedious & repetitive).
A couple of the other Side Quests were fun little activities (aside from the aforementioned Riddler Trophy collection) to break things up; however they too were too short; which would have been fine (since they were side quests after all) if the main story had made up for it; however since the main story was also too short, it almost felt as though the main plot was just an extended side quest itself. So the side missions were fun, but they didn't improve the game enough to make up for the lack of main story.
I liked the fact that they put in a "New Game Plus" feature, and initially was looking forward to playing the game through a second time, but then discovered that the "New Game Plus" feature removes the Counter icon, and I had no desire to play through a second time without that feature. I understand that "New Game Plus" is supposed to be a challenge, but playing without the Counter icon just held no appeal for me; I'd rather the developers had left that as an Option, allowing me select whether or not I wanted to play without it, rather than requiring it. I had no problem with the "Tougher Opponents" in New Game Plus though, that would have been okay, and enjoyable; but the no Counter icon was a deal-breaker for me.
So bottom-line; Arkham City is decent; but lacks depth and has significant room for improvement. Personally, I'd recommend just renting it; you can easily beat the game in a weekend, and get all of the worthwhile content out of it in that time.