As the title advertises, An Autumn War is the war book of the Long Price Quartet. Book 1 of this epic was the romance, Book 2 was the court intrigue, and Book 3 is the blood and thunder.
As with the preceding books, it molds itself around the seasons, shaping plot threads and character arcs around themes of death, renewal, and the cyclical nature of life. Abraham is quite good at this, as became quickly apparent in A Shadow in Summer (Book 1), which I called "an intimate epic". Abraham's focus on character is unwavering, and many of his protagonists are interesting enough that you really do care what happens to them in the end. Even as the geographic scope of the story widens in this war book, each plot thread is motivated almost exclusively by the desires and frustrations of the various protagonists. In other words, the author never loses that focus on character even when he needs to outline the grand movements of clashing civilizations.
Without getting too spoilery, here are the main points: An Autumn War follows Otah, Maati, Cehmai, Kiyan, and Liat as they now enter their 40s, seemingly the autumn of their lifespan. Most of these protagonists now have children (except Cehmai, for he is Machi's poet) and their concerns are directed toward cultivating the next generation. Meanwhile, a new character, Balasar Gice, a brilliant general from Galt, emerges as a dangerous conqueror bent on upending the world order.
This novel, by itself, carries the story through to a truly thunderous conclusion, sounding faint war-drums in the beginning and slowly bringing the horrors of war closer and closer to the people we identify with as "the good guys", until the terror and violence become overwhelming. Still, not everyone dies, and the stage is set for the final book of the quartet (The Price of Spring). So, as far as this single book goes, it is very good by itself and might almost be read successfully as a stand-alone (but why would you do that?).
As part of the quartet, this book is even better. It adds new layers of symbolism to its ongoing meditations on the seasons, and it continues building its world, further articulating the Cities of the Khaiem while introducing the Galts and the peoples of the Westlands and Eddensea. As for the andat... well, I don't think I can talk about that and avoid spoilers at the same time... let's just say that there are some major changes, and they play into the cycle of the seasons, especially autumn.
Also watch for visual symbols. There is one in the aftermath of the big battle in the middle of the book (involving Otah on the battlefield) and another one some time after the final climactic battle (involving Maati in a cave) -- these two symbols are particularly powerful, the former harking back to another symbol introduced in the prologue chapter of A Betrayal in Winter (a heavily ironic symbol), and the latter seeming to presage hope in the fourth volume while acknowledging the tragedies of the first three. Finally, and most impressively, none of the symbols in these books can be mapped onto a single season, nor do they have valence exclusively with the book that they appear in. They are significant in all the seasons, but, for that, they lose none of their individuality. It's clear to me that Abraham conceived a brilliant idea when he started putting together this series and has brought to the task a great talent for integration, consistency, and beautiful story-telling. I am most eager to read the final volume.