The global opening of Watchmen last weekend - $55.7m in North America through Warner Bros and $27.5m in 45 territories through PPI - was strong, but considered by many commentators to be disappointing.

This, after all, was the most-hyped superhero movie since Iron Man and The Dark Knight last summer and it was expected to open with at least as much as director Zack Snyder's last graphic novel adaptation, 300, which took $70.9m in its first domestic weekend exactly two years ago.

But did anyone see Watchmen' Running to 163 minutes (including credits) - which limited theatres to one evening screening - the film is one of the most ambitious and complex storytelling feats attempted by a major studio (or three major studios, if you count Fox's legal position in the film) in some years.

For those of us who don't know the comic books on which it is based, it takes some concentration to figure out exactly what's going on. No wonder it has been in development for more than 20 years and for most of that time was considered unfilmable.

Watchmen is based on the celebrated series by Alan Moore and Dave Gibbons, although Moore refuses to have anything to do with Hollywood after ugly experiences on films of The League Of Extraordinary Gentlemen and V For Vendetta and had any whiff of his name taken off this film.

But whatever the fanboys might say about Sndyer's translation, it's a gutsy cinematic vision and dares to create an entire mythology for the relatively inexpensive price tag of $130m, not bad by today's blockbuster standards. Acted by a fine ensemble, Watchmen contains moments of brilliance, and some images bring to mind the thrill we felt on seeing 2001: A Space Odyssey or Blade Runner for the first time.

It is also R-rated. Snyder's (and Moore and Gibbons') world sees superheroes as part of the fabric of society, doing as much bad as good. They commit grotesque acts of violence, they have sex (they are even impotent sometimes), they are overweight and angry, and they are determined to end the Cold War by any means necessary, even if that means millions of deaths. Steeped in adult language and content, Watchmen tells its superhero story against a backdrop of 20th-century politics and the threat of nuclear war. It asks questions about war and peace and the notion of doing good. Few mainstream films, at least in my memory, have attempted to encompass so much and demand so much of its adult audience.

Many of us who grew up without a passion for comic books or graphic novels have groaned as Hollywood has turned to them as its chief source of major films. Spider-Man, Superman, the X-Men, Iron Man, the Incredible Hulk, the Fantastic Four, Daredevil and of course Batmanhave all been given lavish film treatments in recent years, and many more are on the drawing board.

But as Christopher Nolan proved with The Dark Knight last year, these films do not have to follow a traditional formula, and his Batman epic was as dirty and sprawling in its portrait of organised crime as The Godfather or Goodfellas.

Most of the awards bodies, including the Academy, chose not to select The Dark Knight for their best picture shortlists even though it was one of the best-reviewed films of the year.

Box-office megahits such as Titanic, Forrest Gump, The Sixth Sense and Ghost have won best picture Oscar nominations in the past, but with The Dark Knight, voters still struggled to get past the man in the batsuit. Superhero movies, they apparently believe, can win sound and effects awards (or even a supporting actor Oscar in the case of Heath Ledger this year) but they just can't be taken as seriously as Chocolat or Crash.

That attitude has to change. Hollywood's majors are not going to stop making these films and, as Watchmen proves, they're becoming increasingly bold, exploring contemporary culture through the comic-book myths in far more sophisticated ways than some of the self- important end-of-year prestige titles.

Sooner rather than later, the conservative establishment will have to accept these films as some of the 'best pictures' around.