As mentioned, it has a vibe of War of the Roses with a touch of Arthurian, sort of. It has magic, but not a whole lot. Magic is more of a narrative tool, at least during the earlier portion of the story. Magic IS there, but it's dark, secretive, and not a common thing in the lands (at least in the 7 Kingdoms).
I would say that you wouldn't have to read the books at all to run this game successfully. You could probably get away with just reading the information in the book, and perhaps even reading some of the information found on the net (westeros.org, wiki, etc) to get a better understanding. Although, I would recommend reading the books just because they are good.
If I had to pick keywords that represent the game.. they would be.. Family, War, Intrigue, Sex, Incest, Backstabbing, Alliances, Friends, Secrets, Swords, Low-Magic, Morales, and Faults. I could probably go on, but that's enough I think. The story isn't about "Good vs Evil" like in a lot of other books, where there is always a "good knight" vs some sort of "evil wizard" type of thing. Instead, a lot of the characters have the good and the bad in each of them. The world for the most part is grey. Even the most vile of people in the books could have some good qualities, so it's always sort of a double-edged sword. You get to see the viewpoints from a lot of different perspectives. I'll say this very vague to not ruin anything, but you start the series from a perspective of a single family, then soon after you'll come from another perspective (family/person). At first you'll say that "Ohh wow, those people are evil!" yet when you flip to their side, they usually have reasons as to what they are doing. In the end I think it makes the reader feel sort of sympathetic to all sides in one shape or form.
Anyhow.. I'm sort of ranting lol.