It goes without saying that Batman: Arkham City is one of the year's finest games. With an excellent combat system and an equally fantastic storyline, Arkham City is everything Arkham Asylum was, with the addition of a much more open world.
That said, it's not without its problems. Users on the Xbox 360 are reporting that the game is eating up their save games, with the files pulling a disappearing act. The problem only exists for the Xbox 360 version of the game, and players who picked Arkham City up on the PlayStation 3 are spared the difficulty.
The exact same problem was present in the Xbox 360 version of Arkham Asylum, which appears to have resurfaced in Arkham City. The problem, however, may not be apparent to most players, as only a minority of players are reporting the issue on the game's official forum. It is however widespread enough (at 201 pages and counting) for developer Rocksteady to take notice of it.
Players speculate that if you start a new game after installing the Catwoman DLC, the problem will not resurface.