I got this game because I thought Arkham Asylum was excellent. It was and still is excellent.
My main gripe with City is they've over-complicated what was once a simple system. Added too many options to fights where the previous system was near-perfect. The only thing I like that they added was countering more than one opponent at a time. The rest is not necessary. Now I have to focus more on the controls than just playing the game.
The story is pretty good thus far (only 2 hrs or so into it) and the open city is quite excellent. The side quests were a good addition, but the quips from the Riddler are missed.
Overall good game, but not as good as the first. They added too much to an already well-done system. At this point I rate it an 8, but could go up or down by the end. I thought Asylum was a 9.5.