"From the visionary director of 300," trumpets the promotional tag-line for Watchmen, to which I could only respond, "Really?" Zack Snyder translated Frank Miller's gritty graphic novel to great box-office success a few years ago, but could you call his achievement "visionary?" The word, it seems, presumes a creative perspective that allows someone to see in the source material what no one else could possibly see. What Snyder had done with 300 seemed more like a case of seeing what everyone else had already seen in the source material, and then getting the hell out of the way.

This is the challenge faced by any filmmaker adapting a beloved piece of pop literature. Fans already know what they think this world looks like -- and in the case of an illustrated work like Watchmen, that's even more true. Chris Columbus plodded through two scrupulously faithful Harry Potter films, aware that any deviation would be met with bleats of protest; ditto Catherine Hardwicke and last year's much-anticipated Twilight. You probably don't want a visionary director when it comes to pleasing devotees of a work that they already consider visionary. What you want, really, is a competent hack.

And, after 20 years of stops and starts in bringing this project to the screen, competent hackwork is mostly what Snyder delivers in tackling the landmark work by writer Alan Moore (uncredited in the film due to an ongoing dispute with the publisher) and artist Dave Gibbons. Set primarily in an alternate-future 1985 -- where Richard Nixon is serving practically as president-for-life, and the Cold War still rages -- it posits an America with a rich history of costumed superheroes. But their exploits have been outlawed, leaving the few remaining "masks" to re-channel their energies. Nite Owl (Patrick Wilson) has settled into a flabby, dissatisfied middle age; the "world's smartest man," Ozymandias (Matthew Goode), works with the nigh-omnipotent Dr. Manhattan (Billy Crudup) on an alternative energy source. And the borderline-nuts Rorschach (Jackie Earle Haley) continues to prowl the night, investigating the death of The Comedian (Jeffrey Dean Morgan) as part of a conspiracy to kill off superheroes.

Snyder kicks things off with tremendous promise, shifting from the killing of The Comedian to a credits sequence that lays out 40 years of history -- including the legacy of a groundbreaking team of 1940s superheroes -- in a series of arresting tableaux. It's a tremendously efficient piece of visual storytelling -- the kind of thing that's almost demanded when you're adapting a work that originally appeared as a 12-issue comic-book series.

The key word being "almost." For the most part, Snyder -- and screenwriters David Hayter (X-Men) and Alex Tse -- cling to their source material, making sure that every sub-plot and bit of back story fits somewhere in their 167-minute running time. There's the extended story of how physicist Jon Osterman became the matter-manipulating living weapon Dr. Manhattan, and the investigation that permanently twisted Rorschach's sense of justice. Some of the most striking images are cribbed completely from Gibbons' art, like a shot of the Martian landscape featuring a crater formation in the shape of Watchmen's iconic smiley face. When it comes to potentially alienating the fan-boys and fan-girls, Snyder risks nothing.

In a way, though, that's actually a fairly risky choice. As constructed, Watchmen isn't exactly heavy on ass-kicking superhero action, though there are a few elaborate fight sequences here. Moore was interested in using the notion of costumed vigilantes to explore nothing less than the fundamental nature of humanity, and what it means to save the world. This is a surprisingly talky, philosophically-inclined narrative, and Snyder maintains a clean through-line to understanding Watchmen's big ideas.

Talky, philosophically-inclined narratives do, however, require a certain level of skill in the cast, and here Watchmen proves pretty shaky. Haley makes for a terrific uncompromising Rorschach, and Crudup effectively conveys Dr. Manhattan's ethereal distance from humanity. But Malin Akerman merely looks fetching in Silk Spectre's skintight latex, while Goode's plays Ozymandias with an excessive smugness that's too one-note. A truly visionary director might have thought about casting actors with more dramatic heft, but maybe that's not the first thing on your mind when you've got an assignment like Watchmen. Those who aren't hard-core fans get to see the adaptation that the hard-core fans demanded -- one where there's no room for a director to make anything "visionary," because he's too worried about making a mistake.

WATCHMEN

**1/2 (two and a half out of four stars)

Starring: Patrick Wilson, Billy Crudup, Jackie Earle Haley.

Directed by Zack Snyder.

Rated R.