First you notice the style. The prose in No Country for Old Men is vigorous, tight, unsparing. This is a change from other McCarthy novels, especially the early ones, including Blood Meridian. There the style was distinctive but often overblown, straining too hard for expressiveness, the right word, the precise image. Here the style is more reduced and concise. Cather talked about the art of leaving things out in her essay "The Novel Demeuble." Hemingway put the craft of reduction to work in his stories and novels. Here McCarthy takes the art of excision to an extreme. Not only does he leave words out. He leaves major events out. The narrative will lead up to them, will lead away from them, but it will not describe them. Instead you know something major has happened by references characters make to it, by the consequences they must face, sometimes by the very absence of characters. As a result, what is arguably the major event in the novel is not in the novel. Its violence is all the more disturbing. We don't see it, but we feel it.
McCarthy is an iconoclast. He is horrified by modern American, by the modern world, not merely in its superficial aspects--how people dress, for instance--but in how they think and act. One of the two main characters is the embodiment of the modern world, and he is a terrifying personage. There is a knee-jerk quality to some of the book's complaints about the modern world, about feminism, for instance. Yet such complaints are aspects of the book's integrity, its honesty. It does not compromise.
The integrity and vitality of this book reminds me of Philip Roth, Flannery O'Connor, Paul Bowles, Saul Bellow.
See http://www.cormacmccarthy.com/