One of the best games this year and in my top 5 games of all time!
I think it won the best action/adventure game of the year and best story line of the year (?)
The main difference between this one is that it is open world and not as linear as what arkham asylum is, at first I wasn't too keen on it, but I love it now!
If you want a game with a great story line, a bit different sometimes in terms of gameplay, great graphics and sound and amazing voice acting, great combat/gadgets system, a game where you actually feel like you are playing as batman then this is the game to get!
EDIT:
And you couldn't really judge batman AA on the demo, really needed to play more than what was offered.
And I would sort of recommend you to play AA first.