Durable enough to titillate.
I Am Legend is not 28 Days Later (my nominee for best horror/thriller of all time), but it is good for the post-apocalypse zombie/mutant genre. Sci-fi great Richard Matheson started it all with his novel in 1954; there have been numerous film versions, such as Charlton Heston's Omega Man, that have not been memorable; and this iteration is artistically less than 28 Days but still fun.
In other words, the last man standing is a durable conceit, good enough to titillate and deep enough to spark existential thoughts about the meaning of life and an individual's place in a seemingly random universe where one person making a difference is still a feckless clich?.
New York City is quarantined for a virus that has either wiped out most of the population or turned them into blood-sucking mutants. A scientist's (uncredited Emma Thompson) cancer cure is the cause of the subsequent plague. Will Smith plays the heroic doctor whose research may defeat the virus, but meanwhile don't go out after sunset, as all George Romero fans know only too well.
The shots of vacant New York are arresting (What else to expect from King Kong cinematographer Andrew Lesnie?) especially for those of us used to the difficulty of finding a cab at 5 PM. Will Smith is credible if not just a little too buff (Guess what? a gratuitous shot of him exercising shirtless!) but not too sentimental over the loss of his family to the virus. The notion that Vermont may be the home to survivors, should there be any, is an amusement to this critic, who fled its unsurvivable winters.
The formula is in tact, the edge of your seat just right for viewing, and those of us lost in reverie over Twilight Zone are revived. Smith, like Tom Hanks in Cast Away, proves capable of carrying off a film almost solo. Not lost to the star-power of Smith is the sub-textual staple of the zombie/mutant genre that AIDS is a global threat or ideological extremism makes us all the living dead.