"Nothing ever ends," offers one of the Watchmen as the ravaged planet burns. Damn right, girlie ? a frustratingly fractured mess of back stories, secondary characters and crippling self importance, the film itself takes 160 minutes to tell us that heroes are flawed.

Back in 1986, when Alan Moore's series first exploded from the panels of a comic book, that concept spat all over the concept of selfless superheroes who only took time out from saving the world to help old ladies across the road and rescue kittens in trees. In a 1985 where Richard Nixon is still in the White House and the US on the brink of nuclear war with the Russians, the outlawed Watchmen are glorified vigilantes. Messed up people with issues of their own, they just like taking out their frustrations by kicking ass. Cleaning up the streets is merely a side effect.

But with the new generation of superhero films from 'The Dark Knight' to 'Superman Returns' focusing on our saviours' hang-ups, 'The Incredibles' nicking the heroes as humans idea and even 'Heroes' stealing chunks of his work, Moore's ideas have the musty smell of a room closed for too long.

That's in large part due to the 20-year development process from paper to screen. With more shades of nothing ever ends, it's passed through the hands of celebrated directors like Terry Gilliam, Paul 'Bourne' Greengrass, and Darren Aronofsky before landing in the bloodied lap of '300' director Zack Snyder.

Unwilling to move the action to present day, tone down the violence, full-frontal male nudity and rampant sexuality to family friendly levels, or trim the story to manageable levels, he could be considered brave. Or just plain stupid. When a man who's imagined futuristic dystopian worlds, possessed forests and 'Don Quixote' as a time travel comedy (Gilliam) calls something unfilmable, you know you're in for trouble.

Yes, even you Zack. Certainly, his recreation of decaying mid-'80s New York is almost as dangerously intriguing as Chris Nolan's Gotham. But the source material kicks him in the balls. Hard and repeatedly. Ostensibly about the retired Watchmen solving the murder of a colleague, the Comedian, the central (frankly rather ropey) story is sidetracked by detours ? a jailbreak here, a mid-air sex scene there ? that may remain true to the graphic novel but offer little in the way of substance.

That's left to the character back stories that pummel the main plot into cowering submission. Again fanboys will drool at Dave Gibbons' artwork finally brought to life but compressing some 3500 drawings into even three hours creates a watered-down pop psychology superhero soapie for everybody else.

The only Watchman with actual powers (thanks to a lab accident, natch), Dr Manhattan is forgetting the human inside (and public decency codes). Silk Spectre II, forced into the family business, has mommy issues and a complicated love life. The bitter comedian, with alcoholic rapist tendencies, is anything but a barrel of laughs. And Ozymandias is just a pompous prick.

It's only the affable Night Owl, complete with greasy hair and Michael Caine's glasses from 1978, and menacing Rorschach who really come to life. Given the most screen time, the unlikely partners ? the former has let himself go a little and has trouble getting it up; the latter is an unhinged sociopath (come on, he wears a hessian bag on his face) ? drive the plot, pack the punches, and actually connect with the audience.

Moore, rightly pissed off by what Hollywood did to his 'League of Extraordinary Gentlemen' and 'V For Vendetta', doesn't want anything to do with Snyder's film. That's an extreme stance to take. The ambitious 'Watchmen' is no disaster ? like the heroes themselves it's merely flawed.