Fans of thrillers will be disappointed by Cormac McCarthy's No Country for Old Men. In fact, they are likely to take it as an affront. I believe that's what McCarthy intended. His message seems to have been, "I know the rules for writing a thriller. Here, let me show you how it's done. And once I've lured you in, I'll change gears and disappoint your expectations, because in the end I don't want to write a thriller."
The first 240 pages (roughly) read like a great thriller in which McCarthy artfully builds up the tension. He carefully stokes the reader's expectations, sweeping one along towards what must surely be a climactic showdown between good and evil. But then McCarthy deliberately smashes it all up. After so many pages of buildup, carefully building the tension and anticipation, he cuts straight from the buildup to approximately 60 pages of anti-climax.
This will leave some readers feeling that they've been misled or tricked. For McCarthy exploits the formulas of this genre to feed the expectation of a classic 'good vs. evil' confrontation. There's the bad-a$# special forces guy (Wells), the hardworking 'nam vet (Moss), the virtuous old sheriff (Bell, a member of the 'Greatest Generation'). But none of these guys get to face off against the arch villain in any satisfying way. They're all cast aside, shown up as being no match for the great evil, the man without a history, Anton Chigurh, who sweeps past them like they're just so many yapping dogs. The climactic fight between good and evil never happens.
The author's message is one of hopelessness and desolation. By the end, all the Sheriff can feel is defeat. There's a Biblical allusion in the penultimate sentence, where Bell dreams of his father making a fire "out there in all that dark and all that cold." I think this alludes to a line in the gospel of John (ch. 1, v. 5: "The light shineth in darkness; and the darkness comprehended it not"). However, this image of hope is crumpled up and discarded by McCarthy. It's just an illusion, part of a dream from which Bell awakens.
I've heard some people complain that McCarthy is too 'preachy' in this novel, but that's true only if you identify his views with those of Sheriff Bell. Bell keeps criticizing the times he's living in, contrasting Texas in 1980 unfavourably with how things used to be. However, I don't take McCarthy to share that outlook; if anything, he subverts it with his references to past wars. E.g., Moss and Wells are Vietnam vets and Bell is a WWII vet. While talking to his uncle near the end of the book, Bell discusses a deceased relative who fought in WWI, and another relative who fought against, and was killed by, native Indians in the previous century. There's also a mention in that conversation of 'Coffee Jack', a 19th-Century Texas Ranger who fought against the Indians and the Mexicans. Indeed, that old war against the Mexicans seems to have continued in the form of the drug wars. Earlier in the book, another sheriff tells Bell that he'd just as soon give all this land back to the Mexicans.
In terms of the plot, there's no need for all these references to past wars. McCarthy throws them in to undermine Bell's nostalgia, the point being that violence and destruction are the way of the world, and that's how it's always been.