Tough, but incredibly rewarding, with fantastic combat system
Honestly, it was Batman: Arkham City at E3 2011 that made me go back to the game and pick it up again. Seeing the new game reminded me of how satisfying the original was, and inspired me to try and finally finish it.
It's VERY tough in the build up to the last boss, and some of the Poison Ivy stuff gets a bit silly - but overall I had a blast. The pacing is superb, and the balance of action, puzzle-solving, and small quests (essentially fetch-quests, though they're mainly switch-flippers) makes for a game that you can play in bite-sized chunks. For dads like me, who have to play at weird times of day, and when I can snag a free hour or two, it's very well put together.