I just picked up Ghosts of Ascalon at about 8 am today, and it's now about 6 and I've finished it. (I was out of the house for a bit, so I'll peg this as an eight hour read). The book is set in the Guild Wars universe, about 200 years after the Guild Wars campaign, and a little bit before the GW2 campaign. It's the first book of a trilogy, and lays out the pieces for GW2.
So, how was it? I'll give it a solid 4 out of 5.
The first half of the novel is mostly getting the characters together, and gives the reader the history of Guild Wars. It talks about the Searing, and the Charr, and the events that lead up to the current plot. Guild Wars has a lot of back story, and the information presented here is important for the story itself. It introduces the different races you can play in Guild Wars 2, and shows the dynamics and prejudices of each of the races (or in the case of the sylvari, the utter lack of prejudices).
It is a quest story, so a lot of it is the characters getting from Point A to Point B, and having to deal with one another along the way. It is a 'rag tag' group, to be certain, and only three characters in the story are recognizable as having 'character classes' -- a norn warrior, a human warrior, and a sylvari necromancer. The other human, the charr, and the asuran, I really couldn't tell you. The book focusses more on the setting and the personalities of the characters, rather than looking at it from the point of view of 'this is what's in the game'. In some ways, this is good -- it makes for a tighter story -- but in other ways I'm a touch disappointed as I wanted to recognize some of the aspects of the game here. (Nobody uses a Signet of Resurrection anymore? Nobody uses a Signet at all? What about Resurrection Shrines?)
That being said, the book was good. There were a few things which struck me as 'off', such as the Charr lands, and how the Charr live. I couldn't see it -- charr farmers? Really? Charr peasants? But, ignoring that, I think it worked very well.
For those who enjoy Guild Wars, this is a good read. For those who haven't played Guild Wars, this is an excellent introduction.