There are going to be plot spoilers here, but the movie's nearly two months old at this point; if you haven't already heard what happens, you haven't been paying attention.
Anyway, Josh Brolin finds $2 million, the leftovers of a drug deal gone bad, and runs off with it. This turns out to be a bad idea, because the money belongs to unstoppable killing machine Javier Bardem, who chases Brolin all across Texas, shooting everyone he meets with a pneumatic cattle-slaughtering device that looks kinda like a bazooka attached to a scuba tank. Sheriff Tommy Lee Jones chases after Bardem, desperately hoping to get to him before he bazookas Brolin in the head. But no such luck, and by the end of the movie, pretty much everyone is dead -- Brolin, Woody Harrelson, Kelly Macdonald, assorted random passersby -- and Sheriff Tommy Lee only survives because he retires and gives up the chase.
I feel sorry for Javier Bardem in this movie. Not only is he saddled with the worst haircut of the movie year, he has been handed the horrible task of playing a Meaningful Symbol instead of a person. Bardem's Anton Chigurh is the walking embodiment of Evil, you see. Oh yes, there is Evil in the world -- implacable, unfathomable, unstoppable Evil. And there is not a damned thing that you can do about it but stay the hell out of its way and hope that it doesn't decide to fuck with you, for if it does, you are toast.
There are no tragic fates in this movie. No one dies because of anything they did or didn't do (well, OK, it was pretty stupid for Brolin to steal $2 million in drug money), or because of any particular flaw in their character. They suffer and die because they crossed paths with Evil. Period.
Now if that strikes you as a profound or surprising message, then you may well find No Country for Old Men to be a deep and meaningful movie. I found it to be a waste of a lot of fine acting (Brolin is especially good, as is Macdonald -- you'd never guess that she was actually Scottish -- and there's a lovely single scene from Barry Corbin) and some gorgeous photography, all in the service of bleak grad-school existentialism: The world sucks and there ain't nuthin' you can do about it. Gee, that was worth spending $12 and 2 hours on.