Watchmen, the latest slick-looking comic book film adaptation, knows all the right tricks and conventions of the genre and packs an unexpected intellectual punch.

It's also violent, dark and unmistakably adult. Set in an imaginary 1985 Nixon era, government-sponsored superheroes have helped the US win the Vietnam war, and now find themselves out of favour in a rapidly accelerating nuclear arms race with Russia.

After one of their own is murdered they launch an investigation, only to uncover an unthinkable plot to end the Cold War.

It's bleak stuff and Zack Synder's Watchmen comes across like a combination of the visceral violence of his wildly successful 300 and the gothic atmosphere of The Dark Knight.

It's dark and gritty with a palpable sense of existentialist despair, but that's part of what makes it so compelling.

Watchmen operates on the premise: ‘what would the private and professional lives of superheroes be like in an un-idealised world?' The results aren't pretty.

Watchmen's heroes are flawed, to the say the least: nihilists, misogynists and psychopaths.

In fact, it's often hard to tell where the heroic ends and villainous begins.

And while the film's temporal shifts can make for something of a bewildering experience if you're not paying full attention, and some of the characterisations could be said to be a little shallow (but this is a superhero movie, after all, so who cares?).

Watchmen's visual flair and cracking pace is more than enough to keep you engaged.

While die-hard fans of the original graphic novel would probably hate this film on principle, for the rest of us, Watchmen is certainly an interesting and unusual take on the increasingly tired-looking superhero genre.

Where Watchmen really succeeds, though, is as a film that cleverly undermines our assumptions about the superhero genre, and as far as what Hollywood has offered us to date, this is the bleakest and most interesting yet.