I don't get the criticism of the ending of NCFOM.
Life is full of *** moments. Not every bad man gets caught. Not every story has closure. Injustices abound. They didn't run out of money on the shoot, they shot a scene for scene adaptation of the actual novel which ends just as ambiguously.
The pivotal line in the book and the movie is the minor character, Ellis, the retired deputy that knew Sheriff Bell's father, uttering to the nearly used up lawman, "Whatcha got ain't nothin new. This country's hard on people, you can't stop what's coming, it ain't all waiting on you. That's vanity."
The brief discussion between the two old timey lawmen captures the seemingly random and relentless nature of evil and how it is not really checked despite the best efforts of good men.
Moral of the story from the perspective of the Sheriff: You do what you can to make your corner of the world a better place, but in the end we are all grist for the mill. The entire notion of "no country for old men" alludes to the not uncommon opinion that only young people are so guileless as to think that they will actually "change the world."
The agnosticism that infuses Cormac McCarthy's works comes in the form of the random(?) chaos that almost claims the hitman Chigurh. The manifestation of self-directed evil is almost killed by a driver failing to obey a red light. Is that God punishing the wicked? Who can say? Seemingly senseless things cut down people all of the time, every day, the good and the wicked alike. Death comes for us all. What you do with your time here and what you believe that allows you to make any sense of things is really up to you.
The lack of a "dramatic payoff" in the movie is a true life echo of what reality is.