This game is getting a lot of bad reviews for being 'more of the same' but not only is that not a bad thing, it's not really true. It's true that the game doesn't make massive strides over Arkham City like Arkham City did over Asylum, but that's mostly because City perfected the core combat and predator mechanics, and if you try to mess with that you're likely to do a lot more harm than good. Regardless, this game introduces several new gadgets which are much better than the ones they're replacing in my opinion., an entire new portion of the city to explore, an entire new game mechanic in case files, and several more subtle differences, mostly in the way leveling up and in games achievements works.
The game has much more Nolan-verse feel to it than the previous two titles, which I personally enjoyed. This younger, angrier, more aggressive Batman is loads more interesting than the ones we saw in AA and AC, as are the main villains. There are several twists throughout that help keep it from getting stale or predictable and it does an excellent job of being an actual origin story and showing you how Batman's relationships are established and developed.
I'll also add that the multiplayer is surprisingly fun. I didn't have high hopes for it when I first heard they were adding it in, but it's actually really well done. It's most fun when you're playing as one of the heroes of super-villains, but it's still fun when your playing just a lowly gang member.
I have only completed the main story quest at the moment but I plan on going back to mop up the side quests and challenges just like in City.
Perfect game that isn't getting the credit that it deserves.