When a cure for cancer mutates, killing off 90% of the planet, Robert Neville (Will Smith), a military scientist, is left alone in New York City with his dog, hoping with every passing year that he can reverse the mutation. Slowly drained of his sanity and growing weary of battling the vampire-like creatures that attack during the night, Neville is losing hope that his nightmare will end. When other survivors start to surface, the revelation stuns Neville, who finds his struggle to remain optimistic is in constant battle with his knowledge that humanity has likely been snuffed out for good.

"I Am Legend" is the third attempt to bring Richard Matheson's 1954 novel to the big screen, coming after the 1964 Vincent Price production "The Last Man on Earth," and the 1971 Charlton Heston curiosity, "The Omega Man." "Legend" is perhaps the first film to be blessed with a budget large enough to render the extensive isolation Neville is facing; the absence of community that slowly eats away at his soul.

Director Francis Lawrence ("Constantine") is a skilled enough stylist to pull off the visual majesty of "Legend," and the finest moments of the picture are easily the sequences of Neville and dog Sam driving around the city streets, interacting with a world frozen in 2009. Hunting deer or shooting golf balls into buildings, Neville has the world to himself in the daytime, employing careful street choreography honed over three years of seclusion. It's a game of boredom and survival, and the balance between the two is where "Legend" finds the strongest dramatic flavor, carefully studying Neville's brittle sanity while upping the tension with the menacing "Dark Seekers" and their escalating aggression toward the viral survivors.

Lawrence asks for total silence during the opening acts of "Legend," not just to amp suspense, but to feel the unnerving stillness in the air. Will Smith answers the call accordingly, putting in his best sci-fi acting work to date as Neville. Smith is game to push the character to the brink of madness as Neville tries to lasso a feeling a society in his life through the use of mannequins and scientific minutiae. It's a robust, toys in the attic performance that takes its time to develop, with Smith offering fantastic work feeling around Neville's thickening depression. It's a gloomy performance, but "Legend" is a gloomy film, miles away from the infuriating "aw, hell naw" work Smith traditionally gravitates toward to protect his golden box office standing.

Frankly, I could've watched an entire film of Neville confronting his despondency, but "Legend" doesn't have the guts to see this mountain of despair all the way through to the end. The third act brings out the beasties as they launch their hunt of Neville and his new "family." What could've been an exhilarating twist is neutered by some of the worst CG creatures put to film since 1998, making these nightwalkers look like crude animation tests rather than state-of-the-art 2007 computer creations. What ever happened to the magic of makeup? "Legend" is ruined by this lack of polish, not to mention a perplexing absence of information detailing what compels these monsters and how some of them seem to benefit from a greater intelligence.

"Legend" slumps to the finish line, failing to locate a pathway to a stimulating, satisfying conclusion. Instead, the film follows its fascination with Catholicism to a natural conclusion, snatching away hope for a powerful exit to match the hypnotically forbidding tone rushing through the material. There's greatness inside "I Am Legend," however it's too much work to act enthused about a film that runs out of gas halfway through.