Revisiting a classic is always a little risky. I've lost count of the number of films that I was convinced would never date, only to revisit them with adult eyes and find them lazy or slow or old-fashioned.

It's the same with a lot of books - Portnoy's Complaint, for example, is a novel that seemed shockingly modern when I read it at 11 or 12, but now seems tired, obvious and terribly hard to get excited about, not least because it opened the door to hordes of lesser imitators. Once exposed to a poor relation it's harder to cherish the original. But even if you are capable of ignoring the bandwagon-jumpers that trail behind something truly groundbreaking, it is rare that years later it will pack the same primal punch it delivered when freshly minted. Fashions, politics, that indefinable Zeitgeisty something that a big hit either taps into or helps to create - all will have changed, changing the impact of the work itself.

If so many films and books fail to meet the criteria my adult self requires from work that thrilled the younger me, then pity the poor comic book. Consider, specifically, the one that helped to break down the barriers of the form and won itself a readership way beyond the confines of comic fandom: Watchmen. Co-created by the writer/genius Alan Moore and the gifted artist Dave Gibbons, Watchmen was first published as a continuing 12-part series throughout 1986-87. It is almost impossible to overstate the impact that its publication had on comics and their place in pop culture history. Today, as the clock ticks down to the release of the major motion picture adaptation (due in March next year), and as I open my copy of Watching the Watchmen, the lavish new book from Mr Gibbons charting the creation of Watchmen, I must ask: is it worth revisiting? Does this colossus of the industry deserve its place in the pantheon of modern literature? Or was it, like the rah-rah skirt and the comedy stylings of Pamela Stephenson, enjoyable only at the time?

You didn't - and in fact still don't - need to know a lot about the history of the American comic book or even the history of this particular project to enjoy it. But for those of us who still live and breathe the four-colour masterpieces of our youth, the back-story is important. Charlton Comics, home of various third-division heroes (E-Man? Konga? The Many Ghosts of Doctor Graves? No, didn't think you'd have heard of them) had recently been acquired by the behemoth DC, home of Batman and Superman. Moore's and Gibbons' plan was to create a new epic that would integrate a gaggle of Charlton heroes into the “DC Universe”. Knowing that every character in Watchmen had a “real-life” counterpart, so to speak, still thrills me and my other fanboys to death: Moore's Rorschach was Charlton's Question, Doc Manhattan was Captain Atom and Nite Owl was the hero formerly known as Blue Beetle.

The originals are all but forgotten now, but the simple power of the superhero myth - the low-rent, simplistic trope that found its audience with the lower classes, the young, the borderline illiterate in postwar America - has a significance that runs deep. We need our heroes, we need our myths, and every so often we need someone to remind us that, in reality, they simply don't exist. Which is what Watchmen did for the generation of fans that grew up on the classic adventures of Batman, Superman and the Flash, and all the other whiter-than-white, too-good-to-be-true American gods.

As a piece of fiction, it's true, there is some loss of impact. Set in the mid-Eighties, its alternate universe echoes the real world of the period, with some exceptions: superheroes walk among us, and the US is closer to nuclear showdown with the Soviet Union than even the most convinced doomsday soothsayer believed. Then, the inference that Reagan's America acted with an imperious and aggressive sense of invulnerability seemed timely and bold. Today, with it being even harder to work out who the “bad guys” are, we almost long for the times when all we had to worry about was the stand-off between the US's belligerent international consumerism and the rather quaint totalitarian communism of the Soviet Union.

But there are so many other issues and themes thrown up and dealt with effortlessly: widespread paranoia, conspiracy theories, self-delusional care-workers, lonely people ill-equipped to deal with the realities of ageing and death, and, of course, the flawed, neurotic “heroes” that populate this alternate reality. All seem as bold and original today as they ever did, and all are given added weight and impact thanks to Gibbons' fabulous mastery of every known trick in the comic book artist's arsenal - and a few new ones borrowed from the movies.

Remarkably, the message never overshadows the sheer fun. Depressing dystopian truth-telling has never been quite so thrilling. I'm tempted to declare it Moore's most successful creation - a story that delivers as entertainment on a level playing field with the very best superhero epics out there*. But what makes this a genre-transcending bona fide masterpiece is that, alongside the pulse-pounding action and suspense, the soap-opera style romantic dilemmas and the story of some good but misguided people trying to apply simple remedies to complex maladies, Moore and Gibbons also manage to deliver a devastating critique that cuts to the very heart of the pitiful, timid male fantasy that is the superhero genre at its purest and worst: muscular men and busty women in tight costumes solving all the world's problems with a well-placed punch or a blast of super-breath.

There's a clue to the complexity of their ambition in the title, a shorter form of “who watches the watchmen”, a quotation from the Roman poet Juvenal. It captures the broad sense of the story itself - the growing unease of the non-super population at the power of their masked protectors - but also manages to comment directly on us, the comic's audience, in that postmodern way we all so loved in the Thatcher years. Who really wants to carry on following the shallow exploits of superheroes when the real story lies deeper? And by forcing the ageing population of comic-book fans to question the genre, to wonder what their beloved comic books would be like if populated by characters that were as complex and flawed as real people, they breathed enough new life into the genre to save it from itself.

In the process they opened the gates for no more than a handful of genuinely interesting new books, but literally dozens of third-rate imitators. Indirectly and unintentionally they saved the artform so lesser talents could try to destroy it even more spectacularly. Whether or not they now feel it was worth saving is the question I'd like them to to turn their attention to. Watchmen 2, anyone?

*The arrival of the Watcher, Galactus and the Silver Surfer in Fantastic Four 48-51, the Kree-Skrull war in Avengers 89-97, the Frank Miller run on Daredevil, and the operatic saga that Steve Ditko created with Stan Lee in The Amazing Spider-Man 31-33 all spring immediately to my mind, as I'm sure they do to yours.