I know I am a few months off for the review on this game but I got Arkham City two weeks ago for just $10. I just want to start this by saying that $10 may have been the best $10 I have ever spent in my entire life! I started playing the game with catwoman and found the combat to be OK. I really was not hooked until I started playing as Batman though. Once I was Batman I just started flying through the city with no direction. The grapple hook is so much fun to use in the game! It got even better once I started to learn the map and actually knew where I was going. The navigating and motion is perfect in this game and I experienced little to no glitches while playing. Combat seems repetitive at first but then you begin to face unique enemies that start spicing it up a little bit.
Now my favorite part of the game is the story. I was so hooked on what was happening next that I could not stop playing! The game is centered inside of Arkham City which is all of Gotham's criminals in one walled off district in the city. Technically it is a city within a city really. The story revolves around a killing disease that Joker has. The disease threatens to kill him so he sends his blood to all of the local hospitals so they will use it and infect everyone else. Among the infected is Batman. It seems as if for part of the game that Joker is on your side but you probably can guess that he is actually working against you! I don't want to give away the ending but it left me wanting more!
In terms of replayability, I think there is a good amount to keep you playing the game for many hours. There are 400 hidden riddler trophies to collect, getting each one of those will take you a very long time. There are many extensive side missions with their own story as well. I found myself hooked on the plot of a side mission at times, so they were definitively done effectively. Once you beat the game you unlock a new mode called New Game+. New Game+ is basically just a harder version of the game. The thing is though, you are allowed to keep all your upgrades and gadgets when you start New Game+ so it is not that bad.
When playing this game you really should not rush through the main story. Pace yourself through it and stop to complete a few side missions or collect some riddler trophies. You will enjoy the experience much more that way. This is one of my favorite games of the year and if I knew it was this good when it was released I would have bought the game for $60.