The year is 1985. Nixon is entering his fifth term as president after leading the U.S. to victory in Vietnam, the Cold War has led us to the brink of nuclear destruction, and the masked superheroes of the world have been forced into early retirement by order of the government. So goes the premise of Watchmen, Zack Snyder’s messy but often fascinating take on Alan Moore’s celebrated graphic novel.

Flawed though it may be as a sort of Cliff’s Notes version of Moore’s defining work, Watchmen is the best feature-length adaptation I can imagine, particularly given Snyder’s unerring faithfulness to his sources. While Moore may never see the final cut – or any cut, for that matter – Snyder’s reverence for his brooding prose and the cynical depths of his vision is unmistakable. He has hardly done the author a disservice.

Because Snyder (300) was forced to abbreviate many of the novel’s labyrinthine subplots – one senses he would have crafted a word-for-word re-creation if given the chance – there will always be some who grumble that Watchmen doesn’t go far enough in bringing Moore’s doomsday fantasy to life. Still others will be overwhelmed (or just plain bored) by the richness of detail Snyder has painstakingly crammed into every minute of a nearly three-hour epic.

Give him credit for the lengths he’s gone to to preserve the integrity of the original story while stripping it down to its barest essentials. Though his narrative doesn’t always soar with the same feral energy as Moore’s writing – one wonders if Snyder might have served his movie better if he’d been more willing to deviate from the playbook, considering that the liberties he does take fit so seamlessly into the story – Watchmen is a grand spectacle that captures the novel’s subversive spirit. No small feat, indeed.

Even the most reverent retelling would be undermined without a capable cast to breathe life into Moore’s conflicted superheroes, and Watchmen benefits from at least two casting coups – Billy Crudup, as the omnipotent Dr. Manhattan, and Jackie Earle Haley, whose Rorschach compensates for his slightness of frame with searing ferocity.

As characters, they couldn’t be less alike. Dr. Manhattan, long ago transformed by a freak accident into a hulking mass of blue atomic particles, finds himself increasingly unconcerned with the plight of mankind, for the simple reason that he himself exists on humanity’s periphery. Recognizing man’s destructive nature and resigned to his extinction, he is unmoved by the prospect of nuclear holocaust, pragmatically turning his attention to the next stage of evolution.

Rorschach has no such luxury. A superhero more by choice than biological design, he is the ultimate vigilante, uncompromising in his pursuit of justice and merciless in his handling of criminals. He is a savage, and as his ink-stained, black-and-white mask might suggest, he sees the world in absolutes – good versus evil, with no in-betweens. Yet the humanity Dr. Manhattan can no longer muster burns more fiercely in Rorschach than in any of his fellow crime-fighters. He is the ultimate defender of the innocent, and though his methods are extreme, his passion to do what’s right – as he sees it – is unmistakable.

Jackie Earle Haley (Little Children) infuses Rorschach with the fearsome intensity he requires, but he pulls off a neat trick in the process, rendering the character so earnest in his naïve idealism that he seems downright sympathetic. He self-righteously clings to his archaic code of honor long after his former partners have hung up their masks – all except Dr. Manhattan, whose only mask is the corporeal form he assumes – because he refuses to dismiss the possibility of a better world.

Dr. Manhattan envisions a better world, too, but his vision doesn’t hinge on man’s salvation. Here, he is largely a CGI creation – a fitting choice, if you think about it – but there is a lingering mournfulness in him that Crudup conveys with his delicate, almost whispery voice. Whether he is lamenting his own detachment from humanity or his increasingly steadfast belief that humanity isn’t worth saving is never made clear, but he remains a compelling figure, frustratingly aloof at times, oddly vulnerable at others.

There are other fine performances in the film – Patrick Wilson and Matthew Goode are standouts as erstwhile superheroes whose careers have taken wildly divergent paths – that help compensate for the film’s sometimes sluggish pacing. But even during its slowest passages, when Snyder seems so determined to honor Moore’s dialogue and expository flashbacks that the film loses its momentum, Watchmen remains a wondrous anomaly, a film whose ideas about heroism and human nature are just as forceful as its most elaborate set pieces.

It’s far from perfect. Watchmen is uneven, littered with moments that fail to evoke the emotions Moore played on as a virtuoso storyteller, and at least one key character, Goode’s Ozymandias, seems underdeveloped. But Snyder’s epic undertaking is also thrilling, affecting and boundless in its ambition – in other words, a worthwhile experience for both the initiated and uninitiated alike.