Even moreso than Will Smith, the star of I am Legend is the New York City created in the wake of a global plague that has wiped out mankind.

The once bustling city is desolate, empty of all other human life, an amazingly atmospheric set through which Smith commutes on his daily hunts, rounds and other excursions. It's an urban jungle in which the lofty skyscrapers and magnificent architecture of the city still jut proudly toward the sky even as nature reclaims it from the ground up and herds of deer roam the streets among abandoned cars. It's stunning.

Smith is Dr. Robert Neville, a military scientist who is at ground zero in New York when a viral cure for cancer suddenly evolves into a virulent plague. So far as he can tell, Neville has a unique immunity to the disease, and he works tirelessly to find a cure long after there appears to be no one left -- in the world, not just the city -- to help.

His only companion is Sam, a loyal and extremely well-trained German shepherd who was left in his arms as a puppy three years before when his wife and child fled the city, an event well documented through a series of flashbacks to the nightmarish evacuation scene. That dog brings more passion and emotion to the story than any number of love interests could manage.

But the city isn't empty, oh no. At night, the streets are filled with the shrieks and moans of the living dead -- not zombies or vampires, but infected humans (a la 28 Days Later) who have been mutated by the plague into mindless, flesh-eating, somewhat fake-looking creatures who burn in the daylight. Neville hunts them for human trials of an endless parade of vaccines derived from his own blood.

Meanwhile, he lives in a large and fashionable apartment/fortress off Washington Square, works in a fully stocked lab in the basement, raids other apartments for supplies and is working his way through the stock at a video store peopled with mannequins.

When Anna (Alice Braga) and Ethan (Charlie Tahan) arrive near the end -- survivors from down south who are heading for a mythical human colony in Vermont -- they say they were lured to New York by Neville's endlessly looping radio broadcasts. One wonders how they got there in their little car, since all bridges and tunnels to the island were destroyed, but that's one of those puzzles the film glosses over without too much thought. What's important here is, they shouldn't have messed with the bacon.

The movie also ignores the puzzle of a single infected "zombie" who seems to be evolving a cunning intelligence that includes training feral zombie dogs and setting elaborate traps of his own to catch the last bit of fresh meat in the city. OK, so he still uses his forehead as a battering ram, but I can't help but think a lot of story potential there was wasted.

But don't let that stop you, either. I am Legend doesn't achieve its full potential, but what it does do, it does very well.

The movie paces very slowly through many of its scenes, particularly in the first half, building tension for an audience that isn't quite sure what to expect. There's very little action, so when something does happen, quite suddenly, it effectively scares the crap out of you far more than buckets of gore could ever do.

As bad as things are for Dr. Neville, they get worse. And, just when you think things might get better, they get worse again.

Smith, meanwhile, plays well as a lone soul, with a Cast Away kind of solitude. It's largely a one-man show, but with a dog and a city backdrop instead of a deserted island and the blood-stained volleyball that kept Tom Hanks company. The saving grace of a film that could have been little more than a shoot-'em-up zombie videogame is the depth Smith brings to the role: his Neville is richly human, haunted by memories, filled with guilt and doubt and a growing insanity.

The experience weakens at the end, however, when it drops the thoughtful approach and strives to become an action/horror blockbuster. The first part of the movie is tense and jaw-droppingly atmospheric; the second part is genuinely frightening; but the conclusion is sadly commonplace, a flimsy ending to an otherwise moving and passionate film.

Editor's Note: The story, based on a 1954 novel by Richard Matheson, has been filmed before, but I haven't seen The Last Man on Earth starring Vincent Price (1964) or The Omega Man starring Charlton Heston (1971) to compare it to.