Absolutely fantastic from start to finish. Nominated it for a Hugo as soon as I read the last page.

Three things it taught me about writing:

• Keeping chapters short not only gives you an excuse to read "just one more," it also lets you do abrupt transitions between place and mood.
• Characters grumbling to each other (or in their heads) can give you a very compact and fun way to explain aspects of the world that are unfamiliar to the reader.
• By shifting the metaphors used to describe a scene, you can sustain a difference of mood between locations. For instance, in a place of death and white, describing a series of building supports as "arched ribs" echoes the feeling you want to convey.