Starring Will Smith. Rated 14A.

It's a rare honour to get to hail a new genre classic. I Am Legend, the latest retelling of Richard Matheson's novel of postapocalyptic survival, offers just that opportunity.

I wouldn't want to spoil the movie by revealing too much about what happens, but the setup seems safe to divulge. It's the near future, in a New York City populated with virus-altered mutants. Like zombies, they seek blood; like vampires, they hide from daylight.

One man is left alive: a military doctor named Robert Neville. By day, Neville seeks other survivors and conducts experiments to see if his rare viral immunity can be developed into a cure. At night, he retreats to his well-fortified lair and has bitter dreams of life before the disaster.

Will Smith plays the doctor. At first, I thought it was a casting mistake. It's not that Smith lacks talent; he's steadily grown from blithe Fresh Prince to muscular leading man and underrated actor. The problem, I thought, was that we are used to seeing Smith save the day. His film persona exudes confidence, keen intelligence, and resilience. But as I Am Legend gradually reveals the true darkness and terror of his situation, it's apparent that only a Will Smith type could plausibly continue to function.

As a horror flick, the movie is harrowing. What I love about Francis Lawrence's direction is not just the requisite scares and aggressive sound design but its moodiness, pace, and restraint. Disturbingly, we also get glimpses of the mutant perspective. Neville is more than a meal: he is a tormentor who callously traps them for experiments.

A special horror reserved for genre fans is the fear that the film will tire of its sadness and yield to a syrupy conclusion. But one does not become legend by taking the easy way out.