This was actually a lot better than I expected it to be, although it was perhaps the cynical part of me that expected it to suck (it's telling that I would still buy the book even though I half expected it to be lame). I bought the Wheel Of Time worldbook back in the day and was disappointed, so that maybe coloured my expectations for this one, but the two couldn't be more different from each other.
In the first place, the art in this book is fantastic. I actually feel a little bit strange even reviewing this book, as I tend to not write reviews for graphic novels that I read, but this had far more writing than it did art, so I count it like I would a novel. The art, however, is one of the main reasons to purchase the book, as it looks incredible. The average level of quality is extremely high, which is impressive given that there are nearly thirty different artists who have work featured in the book (my favourite was probably a fellow named Chase Stone, who drew the incredible Ser Duncan The Tall Vs. Lord Lyonel Baratheon, as well as The Death Of Meraxes). Even if you have no interest in buying this book, you should at the very least do yourself a favour and page through it at some point just to check out the artwork.
As much of an ASOIAF fanboy as I am, though, I am cognizant of the relative weaknesses of a book like this. I love reading about history, and I love fantasy, so a book like this is practically made for me, but I understand that reading 300+ pages of fake history is not going to be everyone's cup of tea. Also, the whole book is written as if it were a history book from Westeros, authored by one Maester Yandel. The authors did a fairly good job throughout of maintaining the sceptical, pedantic, and in some cases rather sycophantic tone of a Maester trying to tell a history and still curry favour with his contemporary political elites. Still, this is going to come off as rather dry to some, and there were a few spots where the quality of Garcia and Antonsson's prose was not up to Martin's standard.
I loved reading about Martin's world, though, and this book takes us to many places never seen in the novels of the main series. I was fascinated by the mysterious legends of fallen Valyria, and also the stories of the fabled empire of Yi Ti, although I was a little disappointed that the cities around Slaver's Bay were conspicuously passed over. The highlight of the book, to me at least, was not the more atlas-like sections but instead the history of all the Targaryen kings ever to sit the Iron Throne. This was incredibly interesting, and I would happily have read a whole book of this type of stuff.
Lots of cool names in here, too, and Martin also gets pretty referential. There were a number of H.P. Lovecraft references (Ib and Sarnath from The Doom That Came To Sarnath, Leng and K'dath in the Grey Waste from The Dream-Quest Of Unknown Kaddath, the Deep Ones from practically every Cthulhu mythos story). There were references to other authors (House Vance is an ode to Jack Vance, House Peake of Starpike refers to Mervyn Peake and his character Steerpike from the excellent Gormenghast trilogy, House Jordayne of the Tor is a nod to Robert Jordan and his publisher, Tor). R'hllor, the Lord Of Light gets his title from the Roger Zelazny novel, I believe. I think Hyrkoon the Hero is a reference to Yyrkoon, a character from Michael Moorcock's Elric stories. Martin gets fairly muppetish with his history of House Tully, as some of the men of that family boasted the names Lord Grover, Lord Elmo, and Lord Kermit. There are probably a ton of other references that I missed, too.
To sum up, a very enjoyable read with beautiful illustrations, although probably something that I would only recommend to hardcore fans of A Song Of Ice And Fire.