The main problem with the books and translation to movies is they would all be depressing as hell with so many good characters dying although Martin sure proved people have a larger tolerance for entertaining PAIN than one would actually think possible. Looking right at you RED WEDDING!
That's the thing really, Martin makes up for the depressing by having great and interesting characters you can relate to, and having amazing dialogue. Plus there is no true good and evil for the most part with the characters in GOT.
The strengths of the Convenant series is the Land itself and as you mentioned the Giants are pretty cool. Foul is a good bad as well. But unfortunately the entire story is centered around Thomas and he's an annoying, whiny, rapist twat. I actually think Donaldson is an excellent writer (his Gap series is one of my favorite sci fi series ever), but his writing couldn't overcome how annoying Covenant was for me.
And that would be a major detriment for it to translate to the movies. With GOT if you hate a particular character there are a ton of other interesting ones to choose to focus on. Thomas Covenant doesn't have that luxury.
This post was edited on 10/17 at 11:22 pm