The initial appeal of the last-man-on-earth movies is the visualization of what the world would look like after everybody’s gone: empty streets, grass growing through sidewalks, mutant vampires skulking in the dark.

You don’t always have the mutant vampires, but they come courtesy of Richard Matheson’s revered novel “I Am Legend,” a book that set the template for many post-apocalyptic movies to follow.

Matheson is an ingenious storyteller who wrote some of the best “Twilight Zone” episodes, and Hollywood has labored to get “I Am Legend” right. There was a version with Vincent Price in 1964, “The Last Man on Earth,” and a wacky one with Charlton Heston in 1971, “The Omega Man.”

The newest version, with its original title intact, is finally here, after many years of development with different stars and directors. And it’s still not right.

At least the bread-and-butter is decent. The opening reels of “I Am Legend” unfold with some spectacular shots of a nearly uninhabited Manhattan, three years after a virus wiped out most of the population.

The lone survivor is, coincidentally, a military scientist (Will Smith) who helped cause the problem. A prologue (featuring a puckish cameo by Emma Thompson) informs us that a cure for cancer has mutated badly, infecting the population at large.

Now Smith’s character roams the streets in a Mustang, accompanied by his dog. He dares not go out at night, because the creatures emerge then. These creatures are the same roaring, open-jawed monsters we saw in “30 Days of Night” and most other supernatural movies lately. (They’d be a lot scarier with a human scream coming out of them.)

Director Francis Lawrence (“Constantine”) lets many early scenes play out without music or dialogue, an effective choice. But the movie doesn’t get any kind of flow going, with distracting and redundant flashbacks, and it bungles the big revelations that come late.

The movie does especially poorly at delving into the spiritual aspects of this situation, and unfortunately that’s where it spends its final half-hour (of a surprisingly brief running time).

Will Smith looks like he’s spent most of the apocalypse at the gym, which I guess is as good a place as any if you’ve got a lot of time on your hands. But the actor is hampered by the screenwriters, who have him doing as many stupid things as smart things.

Well, at least there’s special effects. As slick as the overgrown city looks, you have to wonder why it’s always Manhattan. The city is looking a little overused for post-apocalyptic ruin. Next time, how about Cleveland?