Reason number 17,543 that film is the most powerful artistic medium: How else could you get me to sit and watch Metallica--on and off stage, in and out of the studio, and fully up their own asses--for 160 straight minutes than to make a documentary about them? Everything this band represents is anathema to everything I hold dear about rock'n'roll: They are the opposite of melody, the antithesis of punk, the absence of emotional truth, the number one hesher haven of puppy drowners, bedwetters, and fire starters the world over.

And now they are the subjects of the most riveting rock 'n' roll documentary since Don't Look Back.

Metallica: Some Kind of Monster didn't start out as a revelatory exploration of the nature of collaboration. It wasn't even supposed to be a band documentary in the classic sense; it began its life as an infomercial. Filmmakers Joe Berlinger and Bruce Sinofsky, who had previously directed Brother's Keeper and the stunning Paradise Lost films, were hired by Elektra Records to shoot a 30-minute promo film of Metallica in the studio, which would then be aired on TV to advertise the new album; that way, the band--whose members were barely on speaking terms--could avoid going on tour. But as the sessions went on, it became clear that the cameras were about to capture something else entirely.

Bassist Jason Newsted had recently quit, and tensions were mounting from within. With no good work getting done (the writing sessions, in which all three members and the producer collaborate on the lyrics, are deeply painful) the band started falling to pieces, so its management took the unprecedented step of hiring "therapist/performance enhancement coach" Phil Towle to coax the floundering rock stars out of their shells.

Though the initial sessions seemed promising, Metallica simply lacked the vocabulary for self-examination, and even their $40,000-per-month "coach" (who has a very hard time letting go of his role within the group) couldn't inspire them. Singer James Hetfield eventually bailed on the sessions completely, taking nearly a year off to go through rehab, during which time neither his bandmates nor the filmmakers heard a word from him.

With the future of this megamillion-dollar enterprise dangling in uncertainty, the fundamental insecurity of the rock-band dynamic began to come to light. Drummer and cofounder Lars Ulrich, always the shrewdest, most opportunistic Metallica member, could sense that his band was on the verge of a full-blown breakdown, and rather than shutting the documentarians down, he encouraged them to keep shooting while his partner was away. No one knew what would happen, but whatever it was was sure to be of interest to someone.

For once in his life, Lars Ulrich was right.

To list too many specific incidents from Metallica's group therapy would be to rob the film of its hypnotic allure, but it's safe to say that you've never seen a band reveal itself as nakedly--sometimes intentionally, sometimes not--as they do in Some Kind of Monster. (They all cry, however--even former member Dave Mustaine, who never got over being fired.)

Most rock docs are defined by the degree to which the subjects can be seen performing the role of themselves. Dylan in Don't Look Back is the prime example--as well as the greatest performance--but the principle applies to all rock/film stars, from the great (Mick Jagger in Gimme Shelter, Thom Yorke in Meeting People Is Easy) to the interesting (Jeff Tweedy in I Am Trying to Break Your Heart) to the embarrassing (Bono in U2 Rattle and Hum).

What's fascinating about Metallica's performance is the way it echoes their own reputation as guileless regular dudes. They truly seem incapable of being any other way than the way they are--passionate, masculine, and a little dumb around the edges--which is exactly why fans adore them and haters can't touch them. It also means either that they aren't performing here, or that their performance is the stuff of genius. Either way, the movie won't let you dismiss them.

Because so much time passes in the course of the filming (a chilling graphic for anyone who has ever made a record: "Day 715"), much ground is covered. But every conflict advances the band's humanity, from drumbeats ("It just sounds stock to me") to abandonment issues ("I just don't know how to get close to people"). And while it would be nice if all this energy were being focused on better music--it seems like a lot of work for lyrical ideas like "MUTHAFUCKAZ gettin' in my head"--it's ultimately the musicians frankness and not their dubious artistry that gives Monster its vitality.

Despite the fact that the entire group emerges from the crucible, the film is primarily the story of one member's journey into being okay. I spoke to James Hetfield by phone recently and found him witty, warm, and articulate. The main question I had after seeing the film was whether Metallica's fans were ready to see their heroes crying about their feelings for two and a half hours. Hetfield's response was characteristically straightforward.

"It probably will scare some people," he predicted. "And so be it. We're not doing this to shock people. It's a great mirror for us to see what the hell we're up to and why we are how we are. They've seen the other extreme, which is being on stage, the big, dark, mighty Metallica conquering the world. Whatever. This is the other extreme: the broken, scared, lost, fearful-of-the-unknown Metallica. And you know, people are like that. People are allowed to do that. And we want to be people."