Zack Snyder’s stylish but bloody and violent adaptation of Alan Moore and Dave Gibbons’ celebrated graphic novel pulls no punches as its transports us back in time to a very different vision of the mid-1980s.

Relations between America and the Soviet Union are strained and there is a clear and present danger of nuclear attack.

Richard Nixon is clinging on to power in the White House and costumed heroes are part of the fabric of a society in the thrall of fear and paranoia, reflected in the symbolic Doomsday Clock which edges closer to midnight as tensions increase between the superpowers.

In this politically charged climate, a deadly conspiracy involving the masked crime-fighters unfolds, which could have far-reaching implications for the future of mankind.

Many years after the so-called Minutemen - Captain Metropolis, The Comedian, Dollar Bill, Hooded Justice, Mothman, Nite Owl, The Silhouette and Silk Spectre - watched over humanity, a new team of heroes has taken up the mantle.

The Comedian (Dean Morgan) is the last of the old guard still standing and he is joined by Dr Manhattan (Billy Crudup), Nite Owl II (Patrick Wilson), Ozymandias (Matthew Goode), Rorschach (Jackie Earle Haley) and Silk Spectre II (Malin Akerman). When one of the team is murdered in the film’s bone-crunching opening sequence, the remaining members unravel layers of mystery shrouding the crime. In the process, Silk Spectre II clashes with her lover, Dr Manhattan, the only member of the team blessed with actual superpowers (he can glimpse the future) after an accident in a nuclear lab.

The argument drives her into the arms of Nite Owl II and an exceedingly raunchy sex scene, shot in yet more slow motion, to a soundtrack of Leonard Cohen’s Hallelujah.

Watchmen is clearly a labour of love for Snyder, the writer-director of 300, working from a screenplay by David Hayter and Alex Tse, and he adheres closely to the source text.

The pacing is incredibly slow, even in the action sequences, which rely heavily on slow motion. It is little wonder the film runs to an uncomfortable, buttock-numbing 162 minutes.

There is no doubt that Snyder can orchestrate mayhem on a grand scale. The break-in to a prison is masterfully executed and myriad computer generated special effects are seamlessly melded with live action.

However, the final half hour, dense with philosophical navel-gazing, is especially heavy going despite a very simple, straightforward mystery as the central dramatic thread with an obvious master villain.