Okay, I've been enjoying this series since I started it, but this installment really caught me.
Since the beginning, the plot of this story has also always been its world building; it's a narrative that is centered around a main character whose job it is to discover things about the world and it's particularly fascinating in this book, as you realize more about what the world is (and realize even more that the characters have no context to come to the conclusions that you have, which makes it even more fascinating to wonder how they'll get there).
I only have one book left, although Kirstein is apparently working on book 5 so thank goodness.