Will Smith deserves credit-he is fully capable of absorbing work. In "I Am Legend," based on the 1954 sci-fi novel by Richard Matheson, the actor holds our attention by himself for virtually the entire film.

Director Francis Lawrence skillfully guides Smith around the barren streets of post-apocalyptic New York, which is little more than a sky-high cement graveyard overgrown with weeds. Having your main character stranded alone-"Cast Away"-style-is one way to stress the loneliness of his predicament. But the impressively creepy visual motif of a completely empty NYC really drives the point home.

Lawrence makes the most of the scenario, constantly putting U.S. Army officer Robert Neville (Smith) through the dramatic ringer with his faithful companion, Sam the German Shepard. Whether they're hunting deer between abandoned taxicabs in the streets or hitting golf balls off an aircraft carrier parked in Hudson Bay, the eerie tone permeates every scene.

Matheson's book has grown its own legend, mainly because it was notable for getting inside its protagonist's mind and making an unreal premise seem very real. The tedium of day-to-day life for the last man on Earth made Matheson's book come alive, and the movie succeeds on that level as well.

Scenes of Neville going through the motions of renting a movie at the local video store are priceless. He wanders through the store, browsing for DVDs and talking to mannequins that he has strategically placed there to give himself the feeling of companionship. Smith carries theses scenes with a unique mix of humble humor and sadness, and its impossible not to laugh, however grim his situation may be.

Smith himself displays his usual determination. In his basement, Neville conducts a series of cruel experiments, still trying to solve the mystery/find the cure for the virus that wiped out the human race. It's a noble cause, albeit a little too late, but Neville feels partly responsible for the plague and so he must soothe his guilty conscience while simultaneously saving the world. (The virus was set off originally by Emma Thompson, of all people, despite her having the best of intentions. How dare the British try to cure Cancer?)

While hardly getting into the whole "zombies are people, too" paradox that George Romero mined all these years, Lawrence does make his infected monsters scary. The first two-thirds of "I Am Legend" are what the stupid vampires-in-Alaska flick "30 Days of Night" could have been, had it fully exploited its own high concept. (I will give "30 Days" credit, however, for at least having its vampires played by actors rather than be completely computer-generated.)

Yes, the baddies in "Legend" roar like lions and have the strength of bears, but they still look like CGI creations. The computer-generated special effects and set design blend seamlessly with the footage shot in NYC, but as evidenced by "Beowulf," CGI humanoids still have a ways to go. The creatures don't have the texture and color to feel like they actually occupy the same space as Neville. And since they don't talk, lots of the sicker mind games that Matheson explored in the book fall by the wayside.

The third act is where "I Am Legend" finally, fatally trips itself up-leaving you thinking a lot of less of everything you'd seen before the movie's last 15 minutes. A couple of key revelations seem like they are leading somewhere and suddenly, the film is over. It is as if Lawrence realized that they wouldn't work, and just wanted to cut his losses and quickly end the film. I hesitate to give too much away. It is impossible to analyze a movie without discussing the ending, so let's just say this: "I Am Legend" could have been profound, but instead it just settles for pat.