When “Watchmen” was first published in 1985, it was a revelation, a striking piece of sequential art that pushed superhero comics out of the realm of cheap entertainment and into the realm of literature. There had always been comics for grownups, but “Watchmen” marked the first time members of the capes ’n’ tights crowd were treated with gravity and humanity. The reverberations from “Watchmen,” written by Alan Moore and drawn by Dave Gibbons, continue to be felt, and almost every superhero comic since then owes some debt to “Watchmen.”

This towering legacy made a film adaptation of “Watchmen” a sort of holy grail for comic fans and studio heads alike, and a cinematic treatment of Moore and Gibbons’ massive 300-page graphic novel has been in one form of development or another since the late 1980s. But the epic scope, length and intricacies of “Watchmen” made any sort of adaptation nearly impossible. In the intervening years, Hollywood fell in love with other superheroes, and the genre had its own version of “Watchmen” in 2008 with “The Dark Knight,” which injected the usual cinematic shenanigans with some operatic levels of tragedy and a healthy dose of awesome action.

With the graphic novel of “Watchmen” casting such a long shadow over superhero comics and “The Dark Knight” looming so grandly over superhero movies, what sort of new territory could director Zack Snyder’s hotly-anticipated film adaptation claim? Snyder certainly had his work cut out for him, tasked to please not only fans of “Watchmen” but Hollywood execs hungry for another “Dark Knight”-level success. High expectations like that usually lead either to epic failure or stunning success, but Snyder’s “Watchmen” lands somewhere in the middle, flirting with moments of greatness at points but tripping over itself far too often.

As the title implies, clocks figure heavily into “Watchmen,” and the timepiece that towers over all others is the Doomsday Clock, the symbolic timekeeper that tracks how close humankind is to nuclear annihilation. In the world of “Watchmen,” the year is 1985, Nixon is still in the White House, and tensions between Russia and America have escalated to such a level that a nuclear holocaust is all but imminent. There’s another apocalypse on the horizon, though, one targeting superheroes. When the Comedian (Jeffrey Dean Morgan), a former costumed adventurer turned government spook, is murdered, the masked heroes are on alert. A fixture in public life since the 1940s, colorfully costumed heroes were forced into retirement by the government in 1977, and the intervening years were not kind. There’s Nite Owl, a.k.a. Dan Dreiberg (Patrick Wilson), who traded his cape and cowl for a pudgy physique and depression. His former partner, Rorschach (Jackie Earle Haley), refused to give up vigilantism and continued his psychotic war against criminals. Ozymandias, a.k.a. Adrian Veidt (Matthew Goode), “the world’s smartest man,” parlayed his costumed career into a multi-million dollar business empire. And then there’s Dr. Manhattan (Billy Crudup) and his lover, Laurie Jupiter, formerly known as the Silk Spectre (Malin Akerman). Dr. Manhattan is the only truly super-powered one of the bunch, possessing the powers and abilities of a god. Laurie worries Dr. Manhattan is losing his humanity, while Rorschach worries someone is killing off the only people who might conceivably prevent nuclear war.

And those are just the major plot points. “Watchmen” the graphic novel is a Swiss watch, with dozens of characters and hundreds of actions all working together in tight concert to produce a single running narrative. Fitting all those intricacies into a single film, even with a three-hour runtime, is impossible, and while Snyder gets the major points in there, there’s nothing holding them together. “Watchmen” is, for the most part, all bricks and no mortar.

That’s not to say “Watchmen” doesn’t get some things right. Visually, Snyder absolutely nailed it. The film’s look and production design perfectly capture Gibbons’ artwork in the source material. All the small details Gibbons worked into the comic, from the Gunga Diner restaurant to the ads for Nostalgia perfume, are in the film, and the background is filled with appearances of major and minor historical figures. There’s so much to look at that you may even find yourself distracted from the characters.

Those characters are the first place “Watchmen” stumbles. The performances just aren’t that strong; characters who should be compelling and engaging just aren’t. Akerman and Goode, in particular, are weak, a major shortfall considering the narrative importance of both Silk Spectre and Ozymandias. As Nite Owl, Wilson isn’t much better, and there’s never a real sense of the fear and desperation that drive him back into costume.

For all those shortfalls, though, there are plenty of good performances. Crudup’s cold detachment perfectly suits the increasingly alienated Dr. Manhattan, while Haley revels in the Rorschach’s violent moral absolutism. It’s no surprise, then, that the strongest moments in “Watchmen” concern these characters. The middle section of the film, detailing Dr. Manhattan’s origins and Rorschach’s stint in prison, give “Watchmen” the sort of sweeping scope and gritty, tragic humanism the rest of the film strives for but never quite achieves.

The problem lies partially in the clash between Snyder’s stylistic fetishes and the subtler moral questions that come up as Rorschach, the Comedian and the rest caper about. Questions about impotence in the face of tragedy or whether murder in the name of a greater good is ever acceptable all seem sort of silly when people in rubber body suits are doing mixed martial arts in slow motion. That sort of glossy, graphic violence that Snyder employed so well in “300” just doesn’t work here. Nor does the pacing of the film, with long stretches of exposition punctuated by fight scenes straight out of “The Matrix.” Instead of a sustained jog, the movie feels like a manic sprint interspersed with some long naps.

There are plenty of other areas that falter, as well. The musical choices are clichéd and heavy-handed—did we really need another funeral scene set to “The Sounds of Silence”? The soundtrack either hits you over the head with its weightiness or just seems wholly inappropriate. And while Snyder can create brutally violent action sequences with aplomb, he can’t do sex scenes. When Nite Owl and Silk Spectre have sex for the first time (after some hardcore superheroics), it should be a moment of passion and release. But as with the action, Snyder takes a more-is-more approach, and all the explicit thrusting ends up being ridiculous rather than titillating.

It’s clear that Snyder and screenwriter David Hayter respect and revere the graphic novel, but their slavish devotion to the minutiae of the “Watchmen” universe seems to have distracted them from getting some fundamental filmmaking choices right. Having all the right pieces in their correct places is a good start, but inconsistent craftsmanship and generic parts result in a movie that, like the proverbial stopped clock, gets it right at least a couple times, but never really works like it should.