I agree Its a pretty epic game. I've only just finished their 2 nights ago as i saw a trailer for Batman Arkham City and immediately went out and bought arkham asylum.
Spoiler: The Scarecrow hallucination bits epically the last one where the game supposedly resets and joker is driving the batmobile is actually my favorite bit of the whole game.
I would however out without spoiling the game for anyone like to point out i was a little disappointed with the final boss fight. Was a little anti climatic tbh.
still an epic game though.