Yeah, I know, I'm behind the times, I should have read this two years ago - most particularly because I bought it when the author was at MeCon and then I forgot to get him to sign it.
It was tough work - this is not light reading - but I found it unusually rewarding for such an ambitious book. The plot doesn't really resolve - I may even get the sequel to find out if it does - but I really admired Duncan's delicate handling of linguistics and culture. So many authors get the language thing partly (Stephen Baxter) or completely (Robert Jordan) wrong; but Duncan does have an ear for words and how they may change and re-form over the centuries. Likewise, I was impressed with his confident handling of MacLean's Socialist Glasgow, revolutionary Dublin and the southern Caucasus - not quite at expert level in the latter two cases, but at least free of obvious howlers and successfully engaging my interest to keep me reading.
And I love the basic concept of the Book - indeed, my most serious complaint is that the book wanders away from the Book at the end. No doubt this is resolved to a certain extent in the sequel.
Anyway, a fascinating, rewarding read.