Post-apocalyptic dramas typically come in two varieties: grim and grimmer.

The Road invents a third: darn near suicidal.

Based on the novel by Cormac McCarthy, the film about a father (Viggo Mortensen) protecting his son (Kodi Smit-McPhee) from the horrors of end-of-days America is about as bleak as an end-of-days drama can get.

Director John Hillcoat last made The Proposition, an austere but excellent Western set in Australia.

The Road, meanwhile, is something of a Western itself: After a catastrophe of unexplained origin (earthquakes occur, but no scientific or pseudoscientific reason is offered), the world has turned into a lawless land where gangs scavenge for food, shoes and shelter - in that order.

Cannibalism is rampant. So is rape. Children are especially prized - for reasons that the movie alludes to but, thankfully, never fully clarifies.

The unnamed father keeps a gun loaded with two bullets while dragging a cart of scavenged treasures. Better to die, after all, than to become dinner.

Expertly made and authentically filthy - a thick layer of grime covers everything - The Road isn't enjoyable in the conventional sense. Hillcoat maintains an unrelentingly desperate tone until the final scene, which proves hopeful only in comparison with the long, dangerous journey that has come before.

There's simply no letup - from sequences of father and son huddled over meager meals to flashbacks about the fate of the man's wife (Charlize Theron).

Yet, although The Road isn't traditional as movie entertainment, it is effective. It leaves the viewer with a pit in the stomach from the emotional grind.

Is that a recommendation? Yes - in a way. I have little desire to see The Road again, but I also haven't stopped thinking about it. The movie raises questions familiar to the genre (When is murder justified? Is death preferable?) but poses them within such a disturbing context that they're hard to shake.

Mortensen is particularly effective conveying the desperation of a caregiver who knows but won't admit that he is trapped in a hopeless situation. Although father and son talk about "good guys" and "bad guys," The Road has no heroes. Mortensen's character is simply a hardscrabble survivor.

Although The Road isn't as lyrical as McCarthy's book (how could it be?), it does what adaptations should: capture the spirit of the prose while stripping the story to its rawest, most emotional elements.

It's a worthwhile journey - if you have the stomach for it.