I very much enjoyed both the characters and world-building in this book. Both are intelligent and plausible. Even the villain (or as much of a villain as that person is) acts from his own perspective and for his own reasons, and does so with a plausible amount of common sense.
While the character interplay was excellent, I really appreciated the amount of work that's been put into the things that make this world run, and the consequences -- both political, and pragmatic, and also the natural results of having alchemy and immunities.
This is a lovely, complex book, with worthwhile characters and with a story that leaves the reader urgently wanting to find out what happens next.
Happy endings aren't always happy for everyone, or even endings, and this sequel proves the point nicely. While Iathor and Kessa may be betrothed, they aren't married yet, and even then that doesn't necessarily make a _happy_ marriage, let alone heirs.
A number of the events in this book reference the previous one, or revisit philosophical and ethical problems inherent in the series. This is all to the good, as it makes the story feel more plausible, more something that could happen in a living, growing system, rather than just a single short story. The characters and the ongoing plot developments leave the reader wanting more in this series, and in this universe.