I am one of the Uber Geeks who have read the books (well, those written so far) and I'm also one of the few (it seems) who don't mind some departures from the Book Plot to fit the TV Format.
Two of the highlights for me (apart from the battles, intrigue, backstabbing and sex) are the vast open landscapes used as locations (mainly in Northern Ireland) - and the visual effects. They are effortless, unspottable and seamless.
It's nigh on impossible to tell between what's real and what's an illusion. Much like the plot.
Here's the showreel from the Mackevision Visual Department from Season 4, just to give you a taster of what's possible now.