The game certainly has a ton of strengths, but it has weak points too. The story doesn't seem as good as Arkham Asylum's was, the twist is kind of a disappointment, much of the environment ambience is gone because it's no longer as self-contained, and because it's a prison to begin with, the way Batman restrains and takes out some of the villains, is kinda... well, it feels like he's dealing with them in terms of morality and things that stand in his way, so the whole "whose side is everyone on" sensibilities are lost. One of the things about Joker in the first game, is that as the main villain, he had a constant presence in the game, manipulating everything so it all went perfectly. In this narrative, we just deal with stuff as it comes, and there is no "main villain". Heck, some villains just show up for 5 minutes and that's it. They shoved too much stuff in there.
...EVERYTHING else is 5-star quality. From the way you can "fly" in the game by taking advantage of air currents and grapple points to never touch the ground, the way the new gadgets work, the way the game is harder and you need to be stealthier, the new boss battles... it really is something. Amazing game, glad to have played it, wish there was more.