Most of the first hour of I Am Legend follows the efforts of Robert Neville through his daily routine as the last man in Manhattan. Clever enough to maintain a reasonable facsimile of modern life, Neville spends his days fighting loneliness and avoiding the flesh-eating monsters that now occupy the city. These early scenes, particularly the exterior shots of the ruined city, are enjoyably convincing even if they crib from earlier, better films like ‘12 Monkeys’ and ‘28 Days Later.’

Building on the foundation laid by these earlier films is no crime, but unfortunately the second half of I Am Legend fails to develop any new ideas. Instead, our hero deteriorates after a personal tragedy and is saved (literally and figuratively) by the appearance of another human being.

The film almost ignores the one interesting element that develops in the second half, as one of the monsters (formerly humans, now vampire-like zombies) develops intelligence and begins to ape Neville, turning his own survival tactics against him. In one nice touch, Neville himself misses the first signs of this intelligence, misinterpreting the evidence to make it fit with his hypothesis that the monsters are becoming more feral.

The film drops the ball when it fails to follow up on this, and instead chases a cliche action sequence and an implausible happy ending. I Am Legend isn’t bad, particularly in the first hour, but the makers squandered the opportunity to make a great film.