I'm a school librarian, and bought this book for the library. I started reading it, and haven't been able to put it down since! (the kids haven't got a look in so far!)
The depiction of Glastonbury is more realistic than I've ever seen in a novel before, the characters (especially Woolly, Marco and Rosa) are beautifully drawn and believable, and even the more extreme characters (Rosa's dad, Cromwell) are deftly sketched, and believable. The descriptions of Glastonbury Abbey, and the Tor, are bang on, and the sensitive handling of the main characters psychological problems is unusual in this kind of book (after all, normally characters in this sort of book don't HAVE psychological problems!)
The story is gripping - well written, well developed, and beautifully plotted. I'd unreservedly recommend this book to anyone who knows Glastonbury, is interested in fantasy, or ready to take a step on from Harry Potter!
As an aside, this would make a GREAT TV series!