I think from now on, DWJ is moving off my "buy immediately in hardcover" list. There hasn't now been a book that I haven't been slightly disappointed in since Deep Secret, which was the last of the "true" genius DWJ novels, imo.
This one was okay. I liked the domesticity of it, the focus of the action mostly in one small village. I liked the fact that for once there were healthy relationships between the protagonist and adults; Aidan had a grandmother who loved him and whom he grieves for and then goes to live with his... uncle? cousin?? I can't remember - Andrew, who is nice, and treats him well. The system of magic was quite interesting, but not fully worked out (it seems to be about seeing, but turns into performative speech again at the end). The idea of the "counterparts" was quite interesting.
The overall plot was pretty predictable and seemed... unimportant. The ending was rushed, as often happens in DWJ novels. Most of the characters, other than Andrew and Aidan, seemed more like caricatures than people. There was some rather distasteful attitude towards the overweight and the mentally challenged, and I particularly disliked the reference to the mentally challenged man as fat _because_ there was something not-quite-right about his mind.
It was fun, but nothing earth-shattering. Sigh.