This review contains no major spoilers for A Storm of Swords, but it does outline the basic premise of a few characters' storylines, including two that resolves a cliffhanger from A Clash of Kings, and mention the identity of a new point-of-view character. There are major spoilers for A Game of Thrones and A Clash of Kings as well.
More than 400,000 words long and over 1,000 pages in hardcover, A Storm of Swords is, albeit narrowly, the longest book to date in George R. R. Martin's A Song of Ice and Fire. It's also regarded by many or most of the series' fans as the best book yet, full of the gritty detail, unexpected twists, and shocking deaths that set the series apart from other contemporary epic fantasy. Full the book certainly is, and its most momentous scenes are every bit as wonderful as the fan reaction suggests. But I must confess that to my mind A Storm of Swords is, not the best book in the series so far, but the worst.
Part of the problem is simply its length. There's often a desire among readers to see each book in a series become thicker than the last, and most of the time I share that desire. But 400,000 words' worth of the level of detail Martin provides is something else altogether. It's not that any particular storyline, historical detail, character, location, or miscellaneous piece of description is dull or extraneous; it's that, taken together, they cause the book to bog down a little, in spite of the rapid resolution of so many storylines.
Another distracting element is a reliance on unlikely narrative coincidence. Despite the vast size of Westeros and the scope of the story, point-of-view characters cross paths with each other and with minor supporting characters surprisingly often. The issue here is that Martin has introduced some fascinating secondary protagonists and needs to keep them in the story even when they move away from the primary characters who previously provided our perspective on them. So, out all of the people in all the kingdoms they could encounter, they walk into some of the other primary characters. It's not a fatal flaw, and in a story of this size some contrivance is forgivable, but it is distracting, and runs counter to the realism for which the series is justly praised.
Much of the coincidence and path-crossing involves events in the riverlands, where the bulk of the fighting in this War of the Five Kings has taken place. Unlike some fantasy and historical novels, which treat war and conquest as a game for aristocrats and ignore the consequences for ordinary people, A Song of Ice and Fire is at pains to show the disease, destruction, and death that peasants suffer when the powerful cross swords. This is a noble intention, but I can't help feeling that A Storm of Swords takes it too far, to a point where readers may be frustrated rather than inspired to thought or sympathy. One character spends most of the novel bouncing helplessly between one miserable situation and another, his or her storyline advancing very little.
There's another character who also provides a perspective on the riverlands, but his storyline is anything but static. Jaime Lannister becomes a point of view character in A Storm of Swords, and in terms of psychological complexity he's perhaps Martin's richest creation to date. In the aftermath of a long imprisonment the power and arrogance that have prevented Jaime from confronting the egregiousness of his own behavior are diminished, and his grudging respect for Brienne of Tarth, his captor as he crosses the riverlands, leads him to reexamine some of his infamous crimes. It's nothing so cheap and straightforward as a redemptive arc-- he remains Jaime Lannister, proud, snide, and capable of viciousness-- but it does enrich his characterization, adding notes of tragedy and contemplation to what had previously been a monstrous villain.
Regardless of which side they're on in the great conflict, for many of the series' established characters the events of A Storm of Swords are dark ones. Jaime's brother Tyrion remains a point of view character, and in addition to the disfigurement he suffered at the end of the previous book, he has to deal with his father's return to the city, displacing Tyrion from his powerful position as the Hand of the King. Uglier than ever, and unappreciated for his contributions to the successful defense of the city, Tyrion finds his situation going from bad to worse as the novel progresses.
Mother to one of the other contenders for the throne, Catelyn Stark has her own troubles as the novel opens: a dying father, worry over her son's fate in battle, and guilt over her secret release of Jaime Lannister in the hope of recovering her daughters. When Robb returns, he brings news that makes the desperate situation of House Stark even worse. The youthful King in the North has won every battle, and yet finds himself in danger of losing the war.
Separated by distance from the intrigues of southern Westeros, Jon Snow and Daenerys Targaryen continue their isolated storylines. Jon is posing as one of the wildlings to bring information about their intentions back to his brothers on the Night's Watch, but he discovers that keeping to his vows while posing as a spy may not be as easy as he had believed. The unusual ethics and (sometimes literally) larger-than-life behavior of the wildlings enriches the astonishingly deep milieu of the series yet further. As does Slaver's Bay, the region in which Daenerys arrives early in the book. In need of an army, she considers buying the fiercely loyal, viciously trained troops known as the Unsullied from the slave city Astapor. But such a purchase demands a high price, and the young queen's way of paying it may bring her more trouble than triumph.
All these storylines, and several others, evolve toward a major turning point, the end of the first movement in George R. R. Martin's very long story and the beginning of the second. The last third of the novel is so loaded with vivid sequences and jaw-dropping developments that my other complaints come to seem like quibbling. I do believe that A Storm of Swords is the least of the first five books in A Song of Ice and Fire, but that simply means it's the weakest length in a remarkably strong chain.