Like some of the other reviewers here, I gave up on this book, something which I very rarely do, around page 130 ... but then I returned to it, determined not to let it beat me! I wonder why the first 130 pages or so are so difficult and dense and uninviting, because the remainder of the book, for me, at least, proved to be much more readable.
However, I still found it very lacking overall and can only give it two stars. The very heavy use of italics, capitals and even bold italics (which in the Bembo typeface used in the hardback edition are very bold indeed), is jarring to the eye. Some authors (Nicola Barker included) may think it clever to break typographical conventions, but there is a good reason why those conventions exist!
As others have pointed out, the characters are not particularly likeable; in fact I didn't feel we even got to know them much, despite some of Arthur and Beth's 'back story' emerging right towards the end. For me this made it hard to engage with the story.
Either it is going way over my head, or the tricks and codes in the book, as described in the publisher's blurb and by other reviewers, are massively exaggerated. True, there is a simple code mapping numbers to words which is exposed about halfway, and reappears at the end, and there are some strange page numbers which appear at the tops of pages (while the correct numbers appear at the bottom), but is there really some clever game-playing going on between the book and its reader? If so, I missed it.
Like one or two other reviewers here, I really wanted to like this beautifully presented and ostensibly mysterious book. I have a lot of time for A. L. Kennedy as a critic and social commentator, and she was hugely entertaining at the 2011 Edinburgh Book Festival, but I am coming to the conclusion that she is more entertaining as a personality than she is readable as a novelist -- very much like Will Self in that regard.