It’s the end of the world as he knows it, and Robert Neville is feeling anything but fine.

As a military virologist who might just be the last man on earth, Neville (Will Smith) spends his days cruising the desolate streets of Manhattan, where billboards for Hairspray, Rent and Legally Blonde serve as melancholy reminders of a once-bustling civilization in the final stages of a swift decline. By night, he barricades himself in a Washington Square brownstone equipped to withstand even the fiercest home invasion.

His paranoia is justified. Immune to a manmade virus that has transformed 90 percent of the human race into rabid cannibals, Neville is consumed by his lonely quest for a cure. The problem, of course, is that his subjects would rather use him as lunchmeat than donate their pale, hairless bodies to science.

Inspired by the 1954 novel by Twilight Zone author Richard Matheson, I Am Legend has surfaced on the screen before – as 1964’s The Last Man on Earth, a chilling study of post-apocalyptic loneliness starring Vincent Price, and later as The Omega Man, a middling remake with Charlton Heston. Here, Smith is persuasive as Neville, a man driven to the brink of madness by his prolonged lack of human companionship, and delivers one of the most poignant, understated performances of his career.

The role was initially intended for Arnold Schwarzenegger during his 1990s heyday – Ridley Scott was slated to direct – but Smith, who lends a touch of vulnerability to an otherwise indomitable hero, is better suited to the task. Dispensing with the comic bravado that has become his signature crutch, he lends gravity to a tale that is as much a meditation on the realities of extreme separation anxiety as it is a product of man’s ongoing battle against the legions of the undead.

I Am Legend is a superior thriller when it focuses on Neville’s bid to preserve his sanity in a city where time seems to stand still. Its streets are lined with abandoned cars and overgrown vegetation, its towering bridges leveled. In short, it is a haunting portrait of a fallen metropolis, ingeniously rendered by cinematographer Andrew Lesnie.

Neville makes the most of his barren surroundings, perfecting his long game aboard the U.S.S. Intrepid and making casual conversation with mannequins at the local video store. It is a meager existence, but Smith makes his character’s psychological torment believable. When he loses Sam, his beloved German Shepherd and the one remaining link to the life he shared with his family, he reaches a dangerous breaking point that sets up the film’s explosive finale.

It is then that I Am Legend shifts from an absorbing character study to a tense but familiar monster movie. The biggest problem is the monsters themselves – they are at their creepiest when they lurk in the shadows, emerging ever so briefly in swift, terrifying forays. Once we see more of them, though, they stand revealed as routine CGI creations, crudely animated and unconvincing. In a film of such visual majesty and surprisingly weighty drama, they present an unfortunate and needless distraction.