The war between the forces of Odium, a dark god who desires ultimate power over the Cosmere, and the Knights Radiant is continuing to escalate. The Knights Radiant have conquered the ancient tower-city of Urithiru and are using it as an impregnable stronghold to wage war on Odium's forces. Dalinar Kholin forms an alliance with a skilled general and decides to mount an attack on Odium's armies to the south, whilst his son Adolin embarks on a dangerous mission into the other-dimensional realm of Shadesmar to seek an alliance with the honorspren, a task complicated by ancient crimes committed by humanity against them. Kaladin Stormblessed, the greatest soldier in Dalinar's armies, finds himself granted a leave of absence to deal with his own battle stress and self-doubt. But Odium is not beaten yet and takes advantage of Dalinar's absence from Urithiru to put a bold plan into motion.
Rhythm of War is a lot. It's the latest in a lot of books: this is the fourth of ten planned books in the Stormlight Archive series and the twelfth of a planned thirty-odd books in the wider Cosmere universe. It's a lot of pages: at more than 1,200 pages this is the longest epic fantasy novel published since the previous volume in the series, Oathbringer, which in turn was possibly the longest fantasy novel published in over a decade. It's a lot of characters, with dozens of major and minor characters playing important roles in the story. It's also a lot of worldbuilding, with fabrials and Shardplate and voidlight and stormlight and half a dozen different magic system employing different principles being discussed at chapter-stretching length (not helped by the three-year gap since the last book in the series; keeping the Stormlight wiki on standby during reading may be advisable). This is not a series for the faint-hearted or the short of time.
Rhythm of War is also, it is pleasing to report, a stronger novel than its forebear, arresting a slight decline in quality that the series had been suffering since the start. The Way of Kings was a strong novel which set up an unusual, alien setting with an interesting story and worldbuilding and characters who were among Sanderson's best. Words of Radiance was almost as good, but suffered some pacing issues. These pacing issues became overwhelming in Oathbringer, a relatively simple and focused novel that was diffused and made more complicated than it needed to be by immense amounts of worldbuilding and backstory discussions that, strictly speaking, didn't really need to be in the book.
Rhythm of War shores up a building that was, if not in danger of collapse, starting to list under its own weight. The novel is helped by dropping the completely self-contained side-stories that appeared in previous novels and by setting up very clear stories around its four main characters: Venli, Shallan, Kaladin and Navani (with Dalinar, Wit, Adolin and Lift having reasonably important secondary roles). Each story is told clearly and intersects with the others in a well-laid out manner, with Sanderson expending a lot of energy on making these characters jump off the page more than previously.
It's also a heavy novel, in the sense that both Shallan and Kaladin's stories revolve around mental health, stress, PTSD and other issues revolving around personality disorders and the need for good mental health practice. It's a strong theme that was touched on in the previous books but becomes a major plot point in this novel. It's welcome to see a contemporary issue being fleshed out in a fantasy novel in a respectful and mostly well-handled way. However, given the novel has come out in the middle of a global pandemic and many readers will be suffering stress and pressure as a result, readers should be forewarned going into the book that it is tackling weightier-than-normal themes for the author.
The clear demarcation and semi-equal screen time between the four leads helps tremendously in overcoming the pacing issues from the previous novel (thinking of this more as four much more reasonably-sized 300-page novels, each focused on a strong lead character, helps).
That said, problems remain. There are immense stretches of time, especially in the Navani storyline, where characters sit around and discuss worldbuilding issues between them. The idea of characters in a epic fantasy novel acting like scientists and trying to work out how the magic of the world works in an experimental manner is really interesting, but the novel does feel it goes a bit overboard as we see people using magnets and beakers to try to catch stormlight and voidlight in bulbs and do weird things with them. It's a cool idea that is overindulged in.
In addition, the splitting of time between the characters feels a bit uneven at times, with the Shallan/Adolin/Shadesmar plot benched for the entire central third or so of the novel because the author ran out of things for them to do. That's a reasonable solution and better than giving them filler, but it's a bit odd that Shallan is a such a hugely important character at the start and end of the novel but then completely vanishes between.
There's also a perennial Sanderson problem that he's improved on a lot book-by-book but still pops up at odd moments, namely that Sanderson is traditionally a writer who works from the head rather than the heart. There are sections in this book that do feel more like they've come from the heart, excellent action sequences as characters confront old enemies or moments of major character revelation, but some of the book feels studied, analysed and written with something of an absence of passion. This is particularly notable whenever Odium appears live on-page. The Dark Lord showing up to confront the characters (even in a vision where they can't touch or fight one another) should be a major event, but pretty much every time this happens some kind of odd debate on rules of conduct unfolds; the last such major confrontation has all the tension of Odium and Dalinar debating the small print of a text like two opponents who've paused a board game to check the rules online to see if an odd move is allowed. There is a last-minute, genuinely impressive plot twist that might change this for future books, but that remains unproven for now.
Rhythm of War (****) is a stronger novel than the one that came before it and continues to display Sanderson's strengths to full effect: immensely detailed, convincing worldbuilding, solid action and a logical, considered development of the plot, as well as interesting characters. Some of his weaknesses remain, such as a tendency to overwrite, occasionally getting bogged down in the minutiae of the setting and a lack of writing flair in some scenes which doesn't sell big events as much as they should be sold. But it's hard not to remain impressed by the sheer size and scope of the story he is telling here.