This is one of the earliest post-apocalyptic stories. (Poe and Mary Shelley wrote some earlier ones.) It's short and to the point. Its main thrust is that civilization is less a fortress than a rolling machine with a lot of fragile moving parts, vulnerable to complete breakdown at any time if, say, a virulent plague wipes out almost everybody suddenly.
There are some affecting moments in the elegiac ramblings of the old man who is the last to remember the world before the plague, but too much of the novel is him reminiscing. It's not the most gripping way the story could have been told, though I suppose it is in accord with its Ecclesiastes-like brooding on the folly of man.
The love of apocalypse lies deep in the American soul, rooted in biblical nonsense and nourished by Hollywood endings. It's comforting, in a way. If the party has to end, at least we don't have to endure the humiliating decline as the weeds of stupidity choke out the fragile flowers of learning, and jackasses with bullhorns convince the mob that shitting in the water will make everyone rich. Of course, life is rarely as simple as fiction.