Sci-Fi/Thriller/Action. Will Smith, Salli Richardson, Willow Smith, Dash Mihok, Alice Braga, Charlie Tahan. Director: Francis Lawrence

Based on Richard Matheson's 1954 novel, which inspired the films The Last Man On Earth and The Omega Man, I Am Legend is a post-apocalyptic thriller about the last remaining survivor of a terrible man-made catastrophe.

Francis Lawrence's film opens in 2009 with Dr Alice Crippen (an uncredited Emma Thompson) announcing a medical breakthrough: the creation of a retrovirus to cure cancer.

Spectacular results on test subjects suggest the end to one of history's most deadly diseases. Then the nightmare begins: retrovirus patients exhibit rabies-like symptoms and the scientific community races to quell a pandemic. When the virus becomes airborne, it is only a matter of time before the six billion people on earth are infected.

Fast-forwarding three years, military virologist Robert Neville (Smith) - one of the lucky few with natural immunity to the contagion - is in hiding with his dog Sam in the ruins of the Big Apple.

Every day, he patrols the city hoping for some sign of life, then works tirelessly in the lab in his basement, seeking a cure for the outbreak.

Every night, Robert retires to his fortress-like apartment, trying to block out the screams of the cannibals, the Infected.

When Robert captures one of the Infected as a test subject, he inadvertently ignites a war with Alpha Male (Mihok), leader of these poor, unfortunate creatures.

I Am Legend is half a great movie - specifically the first hour, in which Smith's natural charisma and likeability holds us spellbound. The actor brilliantly conveys the loneliness and fragile mental state of his survivor, who finds comfort in conversations with shop mannequins.

In the same way that Danny Boyle transformed London into an eerie ghost city for his zombie thriller 28 Days Later, director Lawrence achieves a similar metamorphosis of New York. The emptiness is chilling. Once scriptwriters Mark Protosevich and Akiva Goldsman move away from a study of their key player's psychological scars and focus on the battle between Robert and Alpha Male, I Am Legend becomes a second-rate Resident Evil clone.

The computer- generated Infected look just like the zombies from a video game, and equally unrealistic, blessed with gravity-defying powers and superhuman strength.

The final showdown is particularly unsatisfying, unleashing a blitzkrieg of digital destruction to distract attention from gaping holes in the film's strained logic.

THREE STARS