As South Park begins its 12th season this week, the cartoon series about the wild adventures of Colorado fourth-graders has never been less culturally relevant. The creation of writer-director Trey Parker and producer Matt Stone (who between them voice most of the main characters), the story of Stan, Kyle, Cartman and Kenny remains one of the most popular shows on Comedy Central and Canada's Comedy Network. Yet in a way, its time has passed. When South Park debuted in 1997, based on a short film in which Jesus battled Santa Claus for Christmas supremacy, it became what the New York Times described as the "cranky, obscene voice of 1990s slacker culture," spawning a movie and turning Parker and Stone into superstars. Now it's not even the most influential show on its network; South Park can parody Hillary Clinton but The Daily Show can have her as a guest. But instead of being nostalgic for the time when they were on the edge of pop culture, Stone — who handles most interviews for the team — told Maclean's that he and Parker can barely watch the episodes that made them rich: "They're terrible as far as story structure and missed opportunities for great jokes." If he's right and South Park is better now, it may not matter that it's less consequential.

The odd thing about South Park is that it's most famous for things it doesn't necessarily do best. To casual viewers, South Park is known for the running gag about the muffled-voiced Kenny getting killed every week. But the gag became old very fast, and the creators have mostly dropped it: "He's such a prop," says Stone. "He can't really talk." The show is also known for its political humour; because each episode is produced in a week, it can respond instantly to topical events. But Parker has said his best scripts are the ones that focus less on messages and more on "boys being boys." The most popular recent episodes have been almost apolitical: the show won an Emmy last year for a send-up of the video game World of Warcraft, and followed it up with a show about Guitar Hero. South Park still has lots of scatological humour, but much of it is an exaggerated way of making the audience, in Stone's words," kind of remember what it was like to be eight years old."

South Park doesn't have much choice but to emphasize its non-topical side; it's burned through two chances to be a true cultural force. Its late-'90s supremacy was brought to an end when Sacha Baron Cohen's Borat and Fox's Family Guy outdid South Park's racist, obnoxious Eric Cartman on a higher budget. Early in this decade, it seemed as though South Park was about to become relevant again, as political commentators started pointing to Parker and Stone as the leaders of a political movement. Conservatives praised the show for its attacks on anti-smoking activists and environmentalists, and Brian Anderson, editor of the conservative magazine City Journal, published a book called South Park Conservatives: The Revolt Against Liberal Media Bias. Parker and Stone were uncomfortable with being pegged as conservative comics; Stone complains that "as soon as something gets popular, it gets co-opted by somebody saying 'that's ours.' " Still, they seemed to run with the idea for several years, amping up the political messages in the show. But events, and changing political trends, caught up with them: by the time their 2004 election episode portrayed voting as a choice between "a giant douche and a turd sandwich," this pox-on-both-your-houses approach was like a relic of the Clinton era when the show began, already dated in the more polarized Bush era. Michael Cust, an editor for the libertarian blog LibertyinCanada.com, adds that while the show still appeals to libertarians like himself, conservatives turned away when they realized that the creators "don't hold conservative moral values." By the time Parker and Stone did an episode attacking the Republicans for their behaviour in the Terri Schiavo controversy, the South Park Republican craze was over.

Since then, there have been individual newsmaking episodes, like a Scientology spoof that led to the departure of South Park voice actor (and Scientologist) Isaac Hayes. But those are one-off occurrences. When Parker and Stone tried to start a controversy in a 2006 episode about censorship and rioting over images of Muhammad, they were chagrined to discover that the only thing that made the headlines was their attack on another animated show, Family Guy.

What's left for South Park is to concentrate on things it didn't have when it was riding high in the late '90s, like strong characters. Originally the characters were differentiated only by basic traits (Cartman the fat kid, Kyle the Jewish kid, Kenny the kid who dies). But since then, the characters have developed in unexpected ways. An early running gag about Cartman's anti-Semitic slurs against Kyle has turned into a strangely complex relationship, with many episodes — including the three-part "Imaginationland" episode that formed the centerpiece of South Park's most recent season — built around Cartman's obsessive attempts to score a victory over his rival. It's a love-hate relationship that recalls Archie Bunker and Mike Stivic on All in the Family, one of Parker and Stone's favourite shows.

The show has also grown by giving more storylines to characters who were underused in the late-'90s glory years. Several episodes last season focused on Randy Marsh, Stan's macho but neurotic father, or the kids' teacher, Mr. Garrison, who underwent a sex-change operation. But the most important bit of character development is the rise of the boys' classmate Butters, who didn't even speak in the early seasons. Butters, described by Stone (who provides his gee-whiz voice) as embodying "permanent innocence," is out of whack with the hip humour that made South Park a trendsetter; he'd be like a '50s sitcom child if it weren't for the fact that his innocence always gets him hurt and abused. But as one of the most well-defined and likeable characters on the show, he's become useful for stories that would be out of character for the other boys, particularly in episodes where Cartman tries to cheat or exploit him. "You've got to come up with some new characters, with some new ways of looking at the world," says Stone, "or you'll just die."

South Park has also improved visually, even though the characters are still mostly shown from only one angle. Parker and the animators have livened up the bargain-basement animation with shadows, special effects, and elaborate subjects like a Buck Rogers parody or a mock disaster movie about the lives of head lice. Stone says they're doing better than they did on bigger budgets: "If you look at the South Park movie which we did in '99, and then at the Imaginationland thing we did last season, directorially and cinematically it's worlds beyond what we were doing, even in a movie format. Scenes that would have been simple proscenium staging now are these cinematic things. And that's because Trey as a director has grown so much." All this means that no matter how ridiculous the stories get — and they still portray a world where Bono is secretly a talking piece of feces — the core of South Park is strangely conventional. Stone could be describing Friends when he says that a good South Park episode is one that "centres on a really solid story involving one of the characters. Those are the ones that appeal most to us, because we're storytellers at heart." Unable to cause the controversy it once did, South Park has filled a void left by the decline of the sitcom: stories that play off our familiarity with the characters. An episode like last season's "Le Petit Tourette" was funny not because it found comedy in Tourette's syndrome (the issue was dealt with somewhat respectfully) but because it was so in character for Cartman to fake having the disease so he'd be free to say whatever he wanted. South Park by now is mostly about how our favourite characters react in certain situations. It just happens that these situations include facing a mob of homeless zombies or getting illegal immigrants to do their homework for them.

At this point it doesn't seem likely that South Park will ever get back to the cultural position it occupied in the late '90s. For one thing, it doesn't have much of a legacy: whereas The Simpsons spawned many imitators and Family Guy has been successfully copied a number of times (including American Dad, from the same producers), South Park remains a stand-alone hit. Other cheap cartoons with a similar sensibility, including some on Comedy Central (like Li'l Bush), have never been particularly popular. And Parker and Stone are no closer to coming up with a second hit; instead they've announced plans to produce other people's shows, including a U.S. version of Canada's Kenny vs. Spenny. But Stone seems to think that he and Parker benefit from the fact that they don't have to be cultural icons: "We've done it, we've achieved it, so now it's like the pressure's off." If the new season is up to South Park's recent level, it may prove what no one predicted back in 1997: South Park does better work when it's not expected to be cutting edge.