If the Sundance Film Festival for independent movies has an even more serious edge to it this year than usual, then what's J. Lo doing in that SUV, blinding the fans on Main Street as the sun glints off her pink-varnished lips?

The stars show up every year for the movie industry's most freewheeling event, ready to embrace their inner independent spirits, and this year is no exception. Lopez was here with her latest ex-husband-to-be, Ben Affleck, for the launch of a new Project Greenlight, the contest in which an unknown gets $1 million to make a movie. But what's Britney Spears's excuse? She was out at parties bumping and schmoozing; perhaps she's looking to jump-start a career in the indies.

It's happened before. And yet the movie stars couldn't really overshadow the movies themselves, which have been, on the whole, extremely serious, harrowing and even shocking. Two audience members in Salt Lake City actually fainted after seeing "Irreversible," a French film with an eardrum-blasting soundtrack and a graphic, nine-minute rape scene. Robert Redford's daughter Amy co-starred in an experimental film based on improvised dialogue. Oh, yes, and Al Gore showed up to support a movie about the Pill, while two former members of the Weather Underground made the rounds for a documentary about their past.

So serious cinema seems to be the theme of this year's festival, which features movies that investigate the social ills of youth and celebrity culture. There's "thirteen," a buzzmaking film about the lives of two scarily average teenage girls in Los Angeles on a bender toward self-destruction. "The United States of Leland" stars the up-and-coming Ryan Gosling, already a teen heartthrob judging by the hysterics of young women around town, playing a sensitive teenager who commits a horrible murder. That film was bought by Paramount Classics studio.

Other hot tickets have been "The Station Agent," a quietly moving story about human connection starring 4-foot-5 Peter Dinklage as Finbar McBride, a loner with dwarfism, and Patricia Clarkson and Bobby Cannavale as two oddball outsiders. The three find themselves in an abandoned train depot and are drawn to one another despite themselves. The film played to standing ovations at the festival.

Clarkson ("Far From Heaven"), meanwhile, is the unofficial queen of Sundance this year, having appeared in practically every other film on the roster, including "Pieces of April," in which she portrays Katie Holmes's mother on her way to a rancorous Thanksgiving reunion, and "The Baroness and the Pig," in which she plays an American expatriate in Paris who undertakes the Pygmalion-style education of a wild child.

Lions Gate bought "The Cooler," an old-fashioned Las Vegas love story starring the inimitable William H. Macy ("Magnolia," "Fargo") as a luckless loser -- nobody plays luckless losers like Macy -- whose luck is so bad it's infectious. He's retained by a slimy casino owner to cool down gamblers on a hot streak, but when Macy falls in love with a cocktail waitress (Maria Bello), his bad luck turns to good and he loses his "cooling" ability. Fans of Macy's will be surprised if not pleased to learn there is a steamy sex scene with Bello in which much flesh is revealed.

And even Robert Downey Jr. got serious, sort of. He plays a character covered with scabs, enraged at the world, who periodically breaks into '50s-style songs in "The Singing Detective." It's a bizarre remake of an old British series, and with any luck, no other American audiences will be required to see it. That's Sundance: Win some, lose some.

Everyone seems to be talking about "thirteen," which was bought by Fox Searchlight. The film is directed by Catherine Hardwicke, who wrote it with 14-year-old Nikki Reed, one of the movie's two leads. Reed, who looks like she could easily be 20, based the two teenage characters -- the other played by an astonishing Evan Rachel Wood, 15, known to some from the TV series "Once and Again" -- on her own experiences.

Wood plays Tracy, who aches to be friends with the popular and beautiful Evie (Reed). She succeeds only by adopting Evie's contemporary code of teen cool -- wearing thongs that peek out from under down-to-there jeans, stealing clothes from the Hustler clothing store on Sunset Boulevard, using drugs and then selling drugs and indulging in casual sex. Holly Hunter plays Tracy's loving, single mother, whose own past is marked with bad choices; she watches the changes in her seventh-grade daughter with growing desperation.

Hardwicke, who dated Reed's father and has known Nikki from a young age, said she embarked on the project as she saw Reed starting to change in some unsettling ways. "When she was 12, she was waking up at 4:30 in the morning to do her hair and makeup before school," Hardwicke said after one packed screening, which ended with hollers and some tears. "I thought, 'What can I do to get her out of this?' "

Hardwicke tried taking Reed to museums but finally encouraged her to write a screenplay. The idea was to write, perhaps, a teen comedy together, but "thirteen" emerged. Reed said, "A lot of what happens to the character happened to me." Wood, a stick-thin figure with blond hair, said the experiences were familiar to her, too. "It hit the nail on the head." Of being a teenager, she said: "It sucks. Girls are mean, judgmental. Everyone's so insecure." Reed: "Nobody's themselves. Everyone is trying to be somebody, trying to escape."

As a portrait of the challenges of becoming a young woman, as well as the challenges of raising one, "thirteen" seems to have hit a nerve with audiences. After one screening, a tearful woman approached Reed and asked, "Are you all right now?"

Al Pacino lurches into the room with the curve-backed gait of the irredeemably schleppy, having apparently descended into a permanent state of disarray. He wears a rumpled black turtleneck under a rumpled black double-breasted jacket, and his black hair looks like it has been through a wind tunnel.

It's the way he's looked in a lot of movies lately. "People I Know" is only the latest to feature what we might call the post-Pacino Pacino -- exhausted, hyperactive, overextended but ready to give the world one more run for its money. This time he plays Eli, a high-powered publicist in New York beaten down by the dead-end values of his job yet desperate to accomplish something worthwhile before he is devoured by his work.

It turns out that the actor's not even that interested in making movies these days; he has 2-year-old twins and wants to stay in Manhattan. "I'm not ready to go off and do things. I like to keep it close to home," he said in a brief, rambling conversation. But Eli's story "was so interestingly, accurately drawn. I literally had to do it. He's a man who's struggling. It doesn't mean it parallels your life." And yet, he added, "You don't know why you do certain parts, but you can speak through certain characters. I don't ever know why I understand some characters and not others." Pacino's next role, apparently free of schleppiness, is in the military drama "The Recruit."

He takes a sip of water, waves a hand vaguely in the air and shuffles out.

Director Matthew Ryan Hoge spent two years as a teacher in the Los Angeles juvenile court system, where he taught teenagers who'd been charged with murder. He turned that experience into a screenplay called "The United States of Leland," which was then rejected by every production company it was offered to but one: Kevin Spacey's Trigger Street Productions. The Oscar-winning actor signed on to produce and star in the film, which led to foreign and other financing.

But the movie's true revelation is Gosling, a sandy-blond actor who caused a stir at Sundance two years ago by playing a terrifying Jewish neo-Nazi skinhead in "The Believer," a movie that made studios so uncomfortable it was barely released despite having won the festival's top prize.

This time Gosling is unrecognizable as Leland P. Fitzgerald, a scrawny, silent, oversensitive teenager who inexplicably stabs to death the mentally disturbed brother of the girlfriend (Jena Malone) who rejects him. At first Hoge refused to consider Gosling for the part, having seen "The Believer." "I thought, 'This is an amazing guy, but it's not Leland,' " the director said. But when Gosling showed up for a meeting, he was the character: quiet, humble. Spacey plays Leland's father, a successful novelist with a vicious misanthropic streak, and Don Cheadle plays a prison teacher who tries to help Leland understand his acts.

The film "is principally a study of morality," Hoge said during an intense discussion with the director and cast after a packed screening. "We want to believe in good and bad people, but in truth we're always skipping back and forth over that line."

Spacey said: "When you look at events that happen in the United States, students who show up at school and shoot kids, they're framed in such a way as being neo-Nazis, on drugs, anything but a kid like mine or yours."

To help Gosling create the character, Hoge gave him a picture of diminutive Charles Andrew Williams, a 15-year-old California boy who shot and killed two classmates (he never gave an explanation and pleaded guilty to murder). Williams was photographed at his arraignment in an orange prison jumpsuit three times his size.

The cast discussed another teenage killer, Kip Kinkel, who when asked by police why he'd killed his parents and two of his classmates in Oregon would only repeat: "I don't know."

"Young people don't have the ability to process tragedy as adults do," says Hoge. "To me the film is the tragedy of a kid who feels nothing, or everything. He's forced to feel so much, and he projects it onto other people. You have to have the ability to feel empathy, and to know when to say, 'That's not my tragedy.' "

Sixties revolutionaries have come back to haunt Sundance this year. Oliver Stone was here with an exclusive slice of life with Fidel Castro. The HBO documentary is based on 30 hours of rare footage of the Cuban leader, but Stone -- who gained the access after writing an ingratiating, four-page letter that compared his career with Castro's -- allowed Castro to demonstrate his legendary charm without ever pressing him on tough questions involving human rights and political dissent. Some will clearly be uncomfortable with this, but Stone seems unconcerned about any looming criticism over what is a largely favorable portrait of the communist dictator. Stone plans to make a similar documentary with footage of another apparently indestructible revolutionary, Palestinian leader Yasser Arafat, which Stone has already shot.

And who hasn't wondered whatever became of the Weather Underground, those ultra-radicals of the 1960s and '70s? Those who have will be intrigued by the PBS documentary in which a half-dozen of the former revolutionaries -- who carried out a series of bombings before surrendering to the authorities in the late '70s -- explain themselves in "The Weather Underground."

Filmmakers Sam Green and Bill Siegel were curious about a largely forgotten piece of American political history. "I became amazed by the generational cliff, where there were people older than me who knew about the Weathermen and how they felt about them, but younger people had never even heard of them," said Siegel, who is 40.

In the film, Mark Rudd, a former Weatherman and co-founder of Students for a Democratic Society, admits to feelings of "guilt or shame" over his actions, and he talks only generally about his past as an underground radical. But others speak with nostalgia about their motivations and clearly still consider themselves revolutionaries.

Former Weathermen leaders (and husband and wife) Bernardine Dohrn and Bill Ayres came to Sundance to say they had some regrets overall but did not regret their motivations.

"There were 2,000 people a day being killed" in Vietnam, said Ayers, who has written a memoir. "What was the right strategy? What should we have done?"

"Most of the things we said and some of the things we did are inconceivable to me now," said Dohrn, a professor at Northwestern University School of Law, who served a year in jail for refusing to testify against one of her former comrades. "But we felt surrounded by violence."

She added: "I would do it again. I wish we could do it better, smarter." But, she said, "It was not terrorism. We were not terrorists. . . . It was not beyond the pale. We blew up a statue of a policeman, not a policeman."

Others in the film, like '60s scholar Todd Gitlin, beg to differ, and the parallels with a looming war in Iraq make the film seem particularly timely. It will air on public television in the spring. Coincidentally, Sundance founder Robert Redford is developing a screenplay about the Weathermen.

A lighter look at the free spirit of the time came in the lyrically nostalgic "The Same River Twice," a documentary about a group of friends who lived on the Colorado River, where they worked as guides in the 1970s.

One of them, Robb Moss, shot footage in 1978 of that rare and carefree time, when the friends lived mostly naked along the water and reveled in their youth and in nature. The film picks up the lives of five of the guides 20 years later, after they have become parents, lawyers, mayors, environmentalists and various other members of mainstream society. One remained a river guide. Moss is now a professor of film at Harvard.

"I wanted to memorialize this time. This was wonderful; we did this," he said. "The past was a moment when we weren't individuals. We were living in a communal way. There was no name for what we were doing, in our own minds. It was sort of Adam and Eve. And there was time. That was our greatest asset."

Parties, parties, parties: The action this year was all along Main Street, where on one night the statuesque Ivanka Trump and her very rich friends fit right in, since they had a documentary in competition called "Born Rich." It's about -- guess what -- the trials and tribulations of being born mega-wealthy. Trump and her director, Jamie Johnson (of Johnson & Johnson), were let in at the front of the line. They're used to that.

Don Cheadle plays a prison teacher who tries to help a teenage murderer understand his acts in "The United States of Leland."Scenes from a movie festival: Director Oliver Stone with Fidel Castro, above, in a shot from Stone's HBO documentary on the Cuban leader, based on 30 hours of rare footage; stars Jena Malone, below left, Ryan Gosling, Kevin Spacey and director Matthew Ryan Hoge form "The United States of Leland"; Robin Wright Penn and Robert Downey Jr. arrive for the premiere of their indie effort, "The Singing Detective," a bizarre remake of an old British series.Main Street in Park City, Utah, heralds the festival and plays host to the parties that inevitably surround it.