In AO you get to visit Arkham City before it became Arkham City. Basically, it's the same map (a bit extended), except everything looks normal. Seeing some locations in their "glory days" is fun, but not enough to overcome the feeling of deja vu. I had expected to see people (of the non-criminal variety) in the streets, since it was supposed to be a normal part of town, and on Christmas eve, no less. That would have introduced true novelty into the game, but instead WB use the cheap excuse of a city lockdown to keep civilians off the streets. There seem to be fewer surfaces you can grapple onto, so moving around is not as seamless as it was in AC. Also, there are respawning snipers that are a real pain in the butt and further restrict your movement.
Of course, there is a brand new story, and it's pretty good, even great at times (bonus points for referencing The Killing Joke). A lot of effort is put into character development: you get to see a younger, more radical and dark Batman, and his transformation into a more mature man, as well as the beginning of his complex relationship with the Joker. On the whole, however, the story feels somewhat anticlimactic, and the confrontations with some of the major villains are not even part of the main quest.
The combat system has been revised so that now you cannot counterattack while in the middle of attacking someone. It may seem like a slight change, but it makes the combat a lot less fluid. On the other hand, you become so overpowered toward the end of the game that nothing short of a small army can be considered a serious threat. Here, once again, WB are afraid to tread new ground and give the player what they think he wants, even though it makes no sense for Batman to be more powerful in the beginning of his career than at its peak. A bolder developer would have given Batman fewer gadgets and placed more emphasis on stealth, but a bolder developer WB ain't.
The multiplayer also deserves mention. It's very similar to Spies vs. Mercs in Splinter Cell: Blacklist, only it's more like Spies vs. Mercs vs. Mercs, with Batman and Robin being the spies, and Joker and Bane's men being the mercs. As Batman/Robin, you can zoom around the map and take refuge on high points, but are very vulnerable to gunfire and have to be stealthy to survive. As one of Joker's/Bane's men, it plays like a 3rd person cover shooter, where you have to watch out both for Batman/Robin and the opposing gang. You can also get the opportunity to play as Bane or the Joker, who pack an extra punch. It's fun, but there are only four maps, and Spies vs. Mercs feels a bit more thought out, so I would recommend Splinter Cell if you are into that sort of thing.
The review wouldn't be complete if I didn't mention the bugs. It's normal for a game this big and complex to have some, but when they render the first major fight (which happens very early in the game) close to unplayable, that raises some questions. And, of course, there is the infamous Burnely comms tower bug that makes it impossible to unlock a portion of the map for fast travel and very difficult to complete the Enigma side quest. I was thinking of giving the game a 7, but after some consideration, it doesn't deserve more than a 6, not with this kind of issues.
Blacklist feels like a more polished version of Conviction. A rating system has been reintroduced, and this time your rating directly affects how much money you earn and, consequently, how many upgrades you can buy. The missions have been made more challenging with the introduction of heavy infantry, who cannot be dispatched with a single headshot, and guard dogs, which smell you from a distance and alert the guards, unless quickly silenced. On the other hand, you are presented with additional opportunities to boost your rating, like high value targets, who can be captured for a fee, terrorist laptops to be hacked, and dead drops to be collected; there are also optional side missions that you can complete at your leisure. Bodies can now be moved and hidden, which only makes sense. The story is a lot more engaging than in the last game and creates a real sense of urgency, even though some important questions are ultimately left unanswered. What the game sorely lacks is the deniable ops mode or its equivalent, since the campaign missions are pretty linear, just like they were in Conviction. The spies vs. mercs mode that has come to replace it is sort of fun, but it's more action than stealth, and half of the match is played in first person mode, which is inconvenient if you play with an Xbox controller like I do. On the whole, a solid addition to the series, but nothing remarkable.