The third filmization of Richard Matheson’s 1954 novel, about a lone man waging a war against ravenous creatures (here, night-feeding zombies created by a plague that’s affected most humans), is probably the best of the lot. It’s certainly the biggest, as befitting a high-octane action vehicle for superstar Will Smith scheduled for holiday release. And one can be thankful that Mark Protosevich’s script, originally fashioned for Arnold Schwartzenegger and now reworked by Akiva Goldsman, wasn’t made, as planned, a decade ago. A mid-nineties version with the Guvernator is almost too hideous to imagine.

Of course calling “I Am Legend” an improvement on “The Last Man on Earth,” the 1964 cheapie starring staid Vincent Price, and 1971’s “The Omega Man” (with brawny, scowling Charlton Heston in the post-“Planet of the Apes” phase of his career) isn’t saying much. Both had some creepy moments, but were generally plodding efforts. By contrast this version certainly takes advantage of its big budget. The imposing vistas of a Manhattan overgrown with weeds, clogged with abandoned cars, and devoid of people but filled with herds of marauding wildlife are impressively spooky, a striking updating of the similar sequences from 1959’s post-apocalyptic “The World, the Flesh and the Devil.” Unhappily, it resembles that mostly-forgotten movie in other, less positive, ways as well. It too is almost unrelievedly grim and increasingly tedious as it goes along, with a third act that stumbles badly and a coda that’s speciously uplifting.

And it has serious flaws of its own. One involves its CGI-created zombies, howling speedsters that never look less than rubbery and are visually more than a little ridiculous (after three years they’re still wearing tattered trousers). And their constant employment by director Francis Lawrence in crass horror-flick shock cliches doesn’t exactly jibe with the picture’s obvious desire to raise “issues” about the meaning of humanity, the need for society, and the ill effects of misguided science. (Still, to be fair the movie represents a distinct advance on Lawrence’s only previous picture, the atrocious “Constantine”—though not enough of one.)

Another major failing involves Smith, an amiable enough fellow but still more personality than actor, ho, on this evidence at least, simply doesn’t have the skill to hold the screen for an hour and a half pretty much on his own any more than the stolid Price or Heston did. As renowned virologist Robert Neville, who’s doing experiments on the “Dark Seekers” in hopes of finding a way to reverse the unhappy effects on them of the boon-to-bust anti-cancer virus unleashed years earlier (by a doctor played in a cameo by Emma Thompson), he works hard but manages nothing much beyond a generalized intensity. And the character’s sense of isolation, which is the whole point of the enterprise, is diminished anyway by the fact that Smith is actually given some support early on, not only by flashbacks to his family life (with wife played by Salli Richardson and little daughter Marley by Willow Smith) but by his faithful companion canine Sam (played by a German shepherd named Abbey). In the final part of the picture, moreover, he’s joined—in the script’s most ludicrous turn—by a couple of other uninfected humans, Anna (Alice Braga) and a young tyke named Ethan (Charlie Tahan), who conveniently show up just as Robert wigs out and needs rescuing from a determined band of bloodsucking marauders.

But of Smith’s co-stars, most are pallid (even Willow, who has nowhere near the screen presence—or screen time—of her brother Jaden Christopher Syre, who played against his father in “The Pursuit of Happyness”), except for Abbey, who serves the same function of lovable sidekick that Jaden did in the earlier picture and gives easily the most affecting performance of the lot. (Her final scene is calculated to draw tears as only a pooch can—witness Old Yeller.) Apart from those disappointing zombie effects, the look of the film is top-drawer, with a sometimes stunning design by Naomi Shohan and expert cinematography by Andrew Lesnie, though its aural side—from the shrieks of the predators to the score by James Newton Howard—is considerably less impressive.

So what we’re left with in “I Am Legend” is just another glorified B-movie with a handsome production and silly pretensions to significance—and far drearier, less enjoyable an example of the type than the recent “Mist.” When considered along with its mediocre predecessors it raises the suspicion that perhaps Matheson’s book isn’t really such a classic after all.