"I Am Legend," the latest entry in the last-man-alive movie genre, pits Robert Neville against two implacable enemies: profound loneliness and blood-lust zombies.

Will Smith plays Dr. Neville, an Army scientist who is hell-bent on finding a cure for the virus that has virtually erased the world's population and turned most survivors into ashen, light-averse sub-human predators who cower in the dark by day and prowl the night in search of fresh blood.

Neville is one of a tiny minority who are immune, but throughout most of the movie he is unable to make contact with anyone else who has managed to stay both uninfected and alive. Ironically, the mutant virus was touted as a cure for cancer before it went horribly wrong.

Determined to find an antidote, Neville remains in New York City as the only person who isn't either dead or a practicing zombie.

He barricades himself inside his upscale home at night, working in his laboratory, cooking for himself and his faithful dog, Sam, and then sleeping (inexplicably, in the bathtub) with Sam while monsters rampage outside.

Protected by the light of the sun, Neville spends his days hunting deer, fishing in an indoor pond, scavenging empty dwellings, trapping zombies for research, and fruitlessly seeking virus-free human contact.

He borrows DVDs from a deserted shop where he also "converses" politely with costumed mannequins as though they are real people. The latter pastime, like his stern lectures to Sam, is a measure of Neville's deep loneliness.

The doctor's solitary days make for the film's most affecting sequences, not least because of Smith's fine portrayal of someone who is isolated, scared and desperately striving to hang onto both his life and his sanity.

Credit also is due the film's astonishing transformation of New York from throbbing metropolis into a spooky wasteland of overgrown streets, abandoned autos, roaming wildlife, empty skyscrapers that loom like giant tombstones -- and not the slightest sign of the people who once gave the city its life.

"I Am Legend" is the third movie to be based on the 1954 sci-fi novel by Richard Matheson. Earlier versions starred Vincent Price ("The Last Man on Earth") and Charlton Heston ("The Omega Man"). The new production is directed by Francis Lawrence from a script by Mark Protosevich and Akiva Goldsman.

It holds up well until about two-thirds through, when it takes a disappointing turn toward the formulaic: auto mayhem, explosions, a garden-variety zombie home invasion, and so on.

A fellow survivor miraculously appears in the person of Anna (played by Brazilian actress Alice Braga), allowing the writers to indulge in a bit of dimestore theology.

Soon afterward, the story ends as abruptly as if a suit from Warner Bros. had called to say, "This has taken enough time and money. Wrap it up, guys."