Some films punish but also enlighten. Others merely punish. John Hillcoat’s adaptation of Cormac McCarthy’s well-regarded novel falls into the latter category. “The Road” is a grim, tedious slog that goes nowhere emotionally, and it seems endless. Whatever the strengths of the book, they’re not apparent here. What’s left is a dreary post-apocalypse tale of a man and his son struggling to survive in a devastated U.S. that seems little different from the sort of raggedy end-of-the-world rubbish that appears regularly on the Syfy Network.

Flashbacks to some unexplained natural calamity—perhaps the destruction of “2012”—provide the backdrop to the episodic experiences of The Man (Viggo Mortensen) and The Boy (Kodi Smit-McPhee) as they trudge through wasteland, scrounging for food and water and evading bands of roving marauders as they aim for the coast, though why is unclear. Along the way they have a run-in with some murderous “Mad Max”-style thugs; barely escape from a family of cannibals whose cellar is stocked with near-corpses awaiting the butcher’s axe; find a bomb shelter stocked with supplies, where they have an idyllic respite from their journey before moving on again; encounter an Old Man (Robert Duvall) whom they briefly aid; and have to recover their belongings after they’re stolen by a guy (Michael K. Williams) whom they have to decide what to do with after they catch up with him. Finally they reach the sea, in a close combining tragedy and hopefulness that can easily be dismissed as sentimental hogwash. Throughout we’re also treated—if that’s the word—to intermittent memories of their erstwhile happiness with The Man’s wife (Charlize Theron), who ultimately couldn’t bear the results of the cataclysm.

“The Road” is intended as an existential parable about survival, sacrifice, and the love between parent and child, as well as a commentary on human nature reduced to its most primitive Hobbesian state, raising the question whether a vestige of compassion and sympathy can remain in such an inhospitable environment. But it never manages to be either viscerally affecting or intellectually insightful. For all its ponderousness and pretension, it winds up feeling like just a gloomier, drier, and happily shorter cousin of “Waterworld.” If the old saw about the best books making the worst movies has any validity, “The Road” suggests that McCarthy’s tome must be a masterpiece.

Much of the blame must go to Joe Penhall, who adapted the book, and Hillcoat, who found a way to make grimness and violence work in “The Proposition” but here manages a tone of little more than lethargic determination periodically punctuated by ghoulish demonstrations of how low humanity can sink. To be fair, though, it’s difficult to say whether anyone could have brought dramatic heft to the material with this cast. Mortensen has proven a very capable actor, especially when he’s working with David Cronenberg, but he brings little but a generalized stoic perseverance to this protagonist, who’s just an ordinary guy thrust into an extraordinary situation, and in Mortensen’s hands he comes across more ordinary than he should have been. The character seems not so much tormented as devoid of inner life—even toward his son, whom Smit-McPhee plays with a similar lack of passion. The fact that their scenes together are amazingly flat is accentuated by the fact that the film occasionally comes alive when a figure like Duvall’s Old Man appears. The actor is only doing the crotchety shtick we’ve seen before, but at least there’s a sense that something human is actually happening on screen, which the rest of “The Road” never really conveys.

What it does offer is occasionally striking visual imagery, courtesy of Javier Aguirresarobe’s widescreen cinematography, which is shot in color but so drained of it that it’s all in shades of gray. Otherwise the picture is indifferently made, with production design (by Chris Kennedy) and art direction (Gershon Ginsburg) that does nothing innovative with this kind of apocalyptic landscape, which we’ve seen so often before. The score by Nick Cave and Warren Ellis tries to give the material some emotional punch but also winds up merely belaboring the obvious.

Oddly enough, the distributor has decided to release this long-delayed film on Thanksgiving weekend. Probably that’s just an empirical decision, trying to position it for end-of-the-year award consideration. But the juxtaposition of a story that features intimations of cannibalism with a celebration centered on a family feast seems more than a little—if you’ll excuse the word—tasteless. But in another way the timing is appropriate, since most people who sit through this horror picture that’s supposed to be redeemed by a heart it unhappily lacks will give abundant thanks when the journey’s over.