I'm conflicted, because this almost deserves four in my book. But not quite. I liked Sabriel (the first in this series) a lot, and the world and the characters here are just as absorbing and unusual. But it suffers a little from middle book slump for me. Particularly in the ending which might just as well have been followed by a page that said "to be continued..." I'd definitely advise having the third book on hand before embarking on this one.
Also I found the protagonists just a little bit whiney. I see why they are so, but I still found myself getting irritated by it. So.. not an unqualified pleasure, but still a pleasure and I am definitely reading on.