Fire and blood
Although Martin didn't lend his pen to this story, he does appear as a character within it (the learned Maester Martin). And there are easily as many layers here as you'd expect from any tale set in ASoIaF. Unravelling the mysteries of the two characters' shared pasts is only one such layer.
Existing fans will find themselves at the slight disadvantage of seeing several of the main plot twist coming miles in advance, but there are still more that no one will anticipate. There are villainous bastards, royal descendants, scheming lords, sorcerous manifestations ("shadow babies"), and a certain book regarding lineages of the Seven Kingdoms that will seem quite familiar to some.
But the game also hints at elements that even avid readers of the series have only guessed at, and its narrative nicely compliments what fans already know to have happened from reading the first book and watching the show's first season.
Watching the two protagonists get sucked down in an ever more dangerous whirlwind of intrigue, lies and betrayal is easily the game's most compelling aspect. I even found myself returning to previous saves in desperate bids to alter the course of events, like turning back the pages of the books and having things turn out differently.
Unfortunately, besides the five-flavored ending, altering the course of the game's events is about as easy as altering what's in the novels. It makes for a great plot, though ultimately you might feel that your choices are meaningless. Of course, given the source material, that may be the point.