This gets three stars because I enjoy the author's writing style. He pulled me in and made me believe in this universe.
However, halfway through the book, the characters began to annoy me. I stopped liking our heroes. I still liked Gretel at the end, which is weird because I really have no use for sociopaths. Maybe "like" is the wrong word. I still found her interesting and compelling.
I saw the ending coming, which usually doesn't spoil a book for me. It just means I've read a lot of puzzle-filled, meticulous novels. Unfortunately, I figured it out about halfway through, which is when I stopped liking the book as much. The second the children started singing to the Eidolons, I knew.
If I had stopped reading ten, twenty pages before the end, I think I would have given this four stars. There was a natural-feeling denouement, and then Tregillis set up for a sequel which looks to be even darker. I don't usually mind dark stories, but when all light or hope is gone halfway through, the book doesn't seem as interesting.
If the author writes something outside of this series, perhaps I'll pick it up.