It took me a really long time to read this book. I put it off because the state of the world at the end of the second book was so dire and I couldn't see how it could possibly improve, but I'm glad I eventually picked up the courage to read it. 
I really enjoyed seeing how Shusterman resolved the issues he had built up through the course of this book and the whole series. Although a less than perfect solution, it feels like a truly human solution to the state the world is in, and although the situation is completely different to reality, it felt hopeful for humanities ability to pull through crisis and improve the world again. I also enjoyed the continuation of the existing relationships in the series, in particular that between Rowan and Citra, and Rowan and Scythe Rand. 
Finally, this book introduced potentially my favourite character in the series, Jericho. I thought Jeri was an extraordinarily interesting character, who's gender is fluid and dependent on the weather (male in cloudy skies, female in clear). I really appreciated this choice, and Jeri was also an amusing and sensitive character who contributed in many ways to the novel.
Overall, it was a great conclusion to a masterful series.