I have read books 1-4, but refuse to read more for now. I think it is a good series if you like the genre (as I do), but the intervals between volumes has gotten too long. I am waiting until Martin finishes, if he ever does. Am hoping the HBO series will encourage him to do so. He's not getting any younger and I would prefer this not turn into a Robert Jordan "Wheel of Time" type thing.
The HBO series is pretty good so far, although like a lot of people, I think there is too much "skin" at times. I know, it's HBO, but still .... I do not think that most of it adds anything to the plot/storyline. It can be a distraction.