I've read most of his stuff, his new Keys to the Kingdom series is really good too. It's between them and the Sabriel/Lirael/Abhorsen trilogy for my favorite of his works, but Shades Children is brilliant as well. I like the ending of Abhorsen, in that they didn't pull a Harry Potter and re-use stuff that has been a few times before (polyjuice and animaguses now piss me off). I think it was almost a Hound of the Baskervilles type of thing; there's no way I would have guessed at what happened at the end, which for me really made the world of the story seem that much bigger, yet it still managed to tie up the last few loose ends. (I'm doing my best not to put spoilers in this post, for those who are just starting the trilogy)