Will Smith on the town in I Am Legend (Photo: Warner Bros.)

Akiva Goldsman admitted it didn't have to be New York. When crafting the third film adaptation of Richard Matheson's 1954 horror/sci-fi benchmark I Am Legend -- the first two of which, like their source material, take place in Los Angeles -- the Oscar-winning screenwriter considered his long-standing affection for the novel. Then he considered his hometown and how it might look completely abandoned: the supposed only survivor of a viral pandemic roaming its avenue canyons by day and its weedy, echoing landscape teeming with vampires at night.

That pretty much settled it.

"That was something I felt very strongly about," Goldsman said at the I Am Legend premiere Tuesday at Madison Square Garden. "All the previous adaptations are set in Los Angeles, which novelistically is very reasonable and resonant. But in truth, Los Angeles is always abandoned -- even at 3 o'clock on a Thursday. So it doesn't help your storytelling. Moving it to New York is a very formidable story engine. What it does is that behind every scene, the city is working. New York is never empty. It lets you know that the world has changed."

For the entirety of I Am Legend's 100 minutes, directed by Francis Lawrence, that desolation never really gets old. Quibbles abound everywhere else, from aggressive product placement to gracelessly exploitive flashbacks to a third act that's more C.S. Lewis than Matheson. But in both its micro-managed realization of a Manhattan cut off from the world -- bombed-out bridges collapsed into the East River, the Hudson gurgling up from the Holland Tunnel, Fifth Avenue towers cloaked in billowing quarantine plastic -- and that isolation's psychological impact on Army scientist and lone survivor Robert Neville (played by Will Smith), Legend achieves more than just authenticity and entertainment value. It possesses a conceptual loyalty that predecessors in 1964 (The Last Man on Earth) and 1971 (The Omega Man) all but drowned in the mainstream. The film lives (and ultimately dies) by the principle that love it or loathe it, ground-level New York culture as we know it is gone.

As technical accomplishments go, it is among Smith's finest, avoiding the cheap, switched-on populism of his bafflingly acclaimed turns in The Pursuit of Happyness and Ali. Neville has his reality down -- he's about 80 percent conditioned to being the last man alive. The other 20 percent -- the widower, the aesthete who expropriates Van Gogh and Haring originals for his fortified townhouse on Washington Square yet has no one to share them with, the insomniac who curls up with his dog as viral vampires screech around the Village? The purpose? That's the tricky part.

"Normally, there's stimulus and response," Smith told The Reeler Tuesday night. "That's what we function off of in our lives. Something happens, we respond to it. With this film, I had to create the stimulus and response. I had pages and pages of internal dialogue about all sorts of things I was experiencing to try to give my mind and eyes and behavior an aliveness that hopefully people see on camera."

Moreover, he had to do it in Midtown, SoHo, on the West Side Highway -- all arrested in a post-apocalyptic snare of traffic, overgrowth and a silence more genuinely shocking than any of his rampaging, bloodthirsty pursuers. It's a conspicuous shift from 36 years ago; in both literal and symbolic terms, Charlton Heston playing chess with a bust of Julius Caesar in The Omega Man can't compete with Smith shopping for CD's and flirting with mannequins at the defunct Tower Records on Broadway. Other flourishes like Neville's morning routine of watching Today Show reruns (if only Neville, burrowed in his basement lab, could find the cure for Ann Curry) and gas prices pushing $7 per gallon trigger a contemporary endearment while time-stamping our futility for future generations.

"I think ultimately to me it was a story about alienation and isolation, about loss and the objectification of that feeling of loss into this kind of wonderfully metaphoric empty world," Goldsman said. "We all imagine what it would be like to be the last person on Earth; we all feel like that sometimes. But to actually have everybody vanish? That's a rich fantasy. So that, to me, was the thing to hold on to."

Of course, said generations will join our own in wondering what the hell happened to the final 30 minutes, when Neville is rescued from a vampire attack by the mysterious, pious Anna (Alice Braga). Here Goldsman and the script's original writer, Mark Protosevich, patronize their audience for the first time. What's worse, they pervert the spirit of Matheson's novel, which has been occasionally labeled sci-fi over the years not just because of its setting 20 years in the future, but also because its protagonist essentially employs the scientific method to deduce means of survival and salvation. Where vampires had physiological allergies to garlic strung around Neville's house, they had a deep psychological distrust of religious symbols like the cross dangling from Ana's rearview mirror.

The image turns an already loose adaptation on its ear, shifting the focus from Neville's solitary (and ineffectual) deductions to the more complex, richly emotional reach of faith. Goldsman acknowledged it without hesitation. "Whether it be secular or non-secular faith was absolutely irrelevant to us," he told me. "So we simply showed a set of symbols that are resonant, but what we really wanted was to say: To live, you need hope. And hope takes different forms." When Anna solemnly announces that God wants her to persist onward to a rumored survivors' colony in Vermont, Neville spits, "There is no God." But neither he nor Anna nor anyone watching buys it for a second. Call it a spoiler, but it's no coincidence that the most emphatic monolith in the film's final shot is a church steeple.

"It's like any other adaptation," Goldsman added. "You're a filter through which the source material gets passed -- favorably or unfavorably, depending on what people's expectations of the object are. But you can only trust your own affection for a thing and hope it won't be too far astray." Ironic, then, that deserted New York -- a country's diameter away from the heart of Matheson's vision -- should be the most rewarding liberty in a legend we may not have another 50 years to get right.