It follows the book pretty well, but it throws in things that are not in the book - like, for example - [spoiler alert] the relationship between renly and the knight of flowers (i forget his name), or the role the red headed whore has that Theon bangs, and then Theon's attitude toward the starks (now that I'm about 200 pages into CoK I know why) and there are other examples too[/spoiler alert]
I haven't got to the battle scenes yet, but I was hoping for a production a la LoTR - not even close.