The initial great story line together with the developing interesting characters. At times difficult to keep all the threads together but I reread the books whilst waiting for latest offering so managed to keep on top of plot, I think!
The swordplay / medieval theme, castles, great families, alliances et al, I just lapped it up.The concept of the wall, loved it. Even the geography intrigued me, I thought he used map of UK for inspiration.
At first the mention of magic, dragons etc sort of threw me as it was not my usual reading material but I gradually warmed to it although in some chapters it sort of overwhelms me.
All in all, really enjoyed books and even the TV series, just looking for something similar ish to look at next.