I heard about this book (as no doubt did many others) in Lucy Mangan's Guardian column. I was instantly intrigued, found Unbound and happily paid my twenty quid. Having no idea what Coptic binding was, on arrival it did look as if the book wasn't quite finished, but that's a minor quibble and I can understand the economic reasons for doing it.
I loved the idea of the "shadow tongue" and found it surprisingly easy to get into: it's interesting that other reviewers have mentioned reading the book aloud. I think this is definitely another dimension to the enjoyment of the story (audio-book next please?) and it changed the dynamic of reading. I stood up in my kitchen (good acoustics) to speak the words and it was a very different reading experience: I felt I was inhabiting the story, moving through the landscape, engaging with the characters in a deeper and more absorbing way. The self-imposed limitations that Kingsnorth placed upon the vocabulary he used makes the language more blunt and immediate, with little artifice: plain words, plainly spoken and yet still infused with poetry.
Buccmaster is not at all a likeable chap, being pompous, arrogant, shallow and childish. An excellent character! I had to be careful not to compare him to Bernard Cornwell's Uhtred as I had just finished reading one of that series. The imagining of Buccmaster's world is done convincingly and his dialogue with the Old Gods is by turns prosaic and poetic. There is a myth that England was totally Christianised by this time, but evidence shows that old and new beliefs coexisted for centuries, even up to modern times, as Christianity absorbed many of the previous beliefs and traditions.
The radical concept of writing a book in a made-up language was for me totally successful, refreshing and enjoyable. My only question: is there another one coming along anytime soon?