The book begins as a 70's style disaster film, with multiple people going about their daily lives as a plague slowly arrives, devastating America. These characters are likable and unlikable to various degrees, and to my displeasure, most of them didn't die. They lived through the world-wide plague. After about three hundred pages of this, King got bored with the story, killed off his developing villain, created a new villain, this one using magic, and rejiggered the story into some sort road novel with pretensions of being a fantasy novel. After that, the characters all converge on Denver to build a new government, and the tedium grew even more tedious. To my own good fortune, my copy was missing pages 1015-1078, which is where the finale happens. I didn't miss anything.
I didn't care for the first hundred pages, cared less for the second hundred, and my lack of care for the remaining book would require frequent repeated profanities uttered in absolute dejection.
A competent editor could have cut the book in half and nobody would have notice. A very competent editor would have rejected the book, thereby cutting its length by 100%.
This is not an indictment against King. He shows repeatedly what a good writer he is all along the way. The problem lies entirely in the rambling story. His characters which work well in horror novels, where people die for petty reasons, and somebody's got to die first, don't work well as apocalyptic survivor characters. I don't want to see these characters survive the world. There are times when their quest for survival goes from one TV trope to another. As for the fantasy element, that feels like an iron on decal, pressed onto the top of the story because he didn't know any other way to get his characters together. The story feels like a bunch of disparate elements pressed together into a mass, pretending that to be a whole, but constantly reminding you that it isn't a whole at all.
Curious about the ending, I went and read a summary, and that summary made me very glad that I was missing that part of the book.