Oh, I love this book, too, and your review (memoir?) is excellent. I came to this from reading Over Sea Under Stone obsessively (I had an Arthurian thing from ages 7-9), and it was the first time I'd read a sequel that wasn't immediately a sequel. I wasn't predisposed to liking Will, because of that, but he got through via stolid determination, and, as you say, that sense of loss that runs through the whole book.

(I think what you say about the story is fascinating, because yes, plot coupon with the signs; but it's so much more than that! A lot of it is I think not just the sense of home, but the sense of place - not a dimly illustrated fantasy world, but a real community, from Will's family outwards - and again that's all what he'll have to give up)