The thing I really appreciated about this book is how...easily pushed around it showed me to be. When Misery was fighting in one direction, I was desperately rooting for them to believe. And once they did, I was desperately rooting for them not to believe. 
The story itself is complicated and I thoroughly enjoyed that the book wasn't necessarily interested in revelations as they occurred to the characters, but understood that the reader's attentions and the characters are just radically different because it's a story about how to craft the story of the hero.
And it's also very much a story about the mechanisms of faith—not faith itself exactly, but how faith works within the human mind. What makes people come to believe and what is it that distinguishes real faith from false beliefs. What is compelling, what is simplistic, and why do things look the way they do through different lenses?
And what Yang does with the Larex Forge and the mythology here is create a theological gedanken experiment where, given the nature of the book's reality, divinity might be real or might be madness and you can infer only from what the book tells you. Which is particularly fascinating to me because of what it reveals about when and what I want to believe.
Also, like, giant space mechs shaped like horrifying angels.