It's impossible to watch "Metallica: Some Kind of Monster" without recalling "This Is Spinal Tap." If Rob Reiner's 1984 comedy classic is still the greatest fake documentary about a fake rock band, "Some Kind of Monster" gives it a run for its money as a real documentary about a real rock band.

Indeed, there are so many scenes of aggressive posturing and unintended humor that at times Metallica threatens to out-Tap "Tap." But by the end of this absorbing, funny, exhilaratingly entertaining ride through two years in the life of the most successful heavy metal band in history, the musicians have revealed themselves not as a bunch of posers but as surprisingly intelligent and appealing middle-aged businessmen and fathers, who happen also to be incredibly gifted musicians.

"Some Kind of Monster" begins in 2001, at a turning point for Metallica. Formed in 1981, the band eventually became the biggest-selling and most respected heavy metal band in the country, selling nearly 90 million records over two decades. But as the movie opens, the band hasn't recorded in several years, bass player Jason Newsted has just quit and it's recently alienated thousands of fans by suing them for downloading their music through the file-sharing service Napster.

Tensions within the band -- now composed of drummer Lars Ulrich, lead singer and guitarist James Hetfield, guitarist Kirk Hammett and producer Bob Rock, who's sitting in on bass -- have reached such a pitch that its managers have hired a therapist and performance coach named Phil Towle to help the members work through their issues.

"Some Kind of Monster" sits in on group therapy meetings, recording sessions, individual soul-searching and forays out into a world that the musicians occasionally fear has passed them by.

Trying to make an album that sounds like guys "getting together in a garage for the first time," they clearly want to stay true to the loud, fast, thrashing sound that made them multi-millionaires, but they don't want to be a dinosaur act. What's more, they want to change the way they've been creating songs. Heretofore, Hetfield has been responsible for all of the words; now, as a result of their sessions with Towle, they collaborate, often uneasily, on lyrics that sometimes resemble the schoolbook marginalia of an angry ninth-grader.

As fascinating as the creative process is, the core of "Some Kind of Monster" lies in the therapy sessions with Towle, wherein Ulrich and Hetfield work out their latent hostility and the long-suffering Hammett plays constant conciliator.

And once in a while, an old friend drops in for a chat. In one of the movie's most discomfiting scenes, the band's first guitarist, Dave Mustaine, confronts his old mates with his lingering feelings of shame and humiliation at having been kicked out of the band. This turns out to be a piece of canny foreshadowing: Later, when Hetfield is in rehabilitation for alcoholism and the rest of the band isn't sure Metallica will survive, they go to see Newsted's new band and are blithely ignored by the bassist and his entourage -- which used to be theirs.

"Jason is the future," Ulrich says miserably. "Metallica is the past."

Is Ulrich right? Will Metallica survive? Can it make one more hit record? If "Some Kind of Monster" is propelled by such high-stakes drama, it is kept afloat by scenes of devastating humor, as when a newly recovered and still heavily tattooed Hetfield leaves a recording session to attend his daughter's ballet recital, or when Towle, Yoko Ono-like, silently passes the guitarist suggested lyrics on a Post-It note. Indeed, the film takes an altogether "Tap"-like turn when it becomes obvious that over several intense months Dr. Phil has come to believe he's joined Metallica -- to the point of selling his house in Kansas City to move to California.

Such moments are fraught with opportunities to poke fun, as filmmakers Joe Berlinger and Bruce Sinofsky did in such previous films as "Brother's Keeper" (1992) and "Paradise Lost: The Child Murders at Robin Hood Hills" (1996). But here they exhibit too much compassion and respect for their subjects to resort to cheap shots. Rather, they give every man his due, creating a film that, even at its most funny and revealing, never compromises anyone's dignity. (As it happens, Metallica helped fund "Some Kind of Monster," but gave the filmmakers final cut and insisted on no major changes during post-production.)

Because it's been made with such a judicious and assured hand, "Some Kind of Monster" transcends its immediate subject to become a surprisingly profound examination of relationships, creativity and the anxieties of encroaching age. By the end of their arduous but ultimately rewarding journey, these brave, talented, indefatigable men might paraphrase their idols, the Rolling Stones: It's only rock-and-roll, but they can deal with it.

Metallica: Some Kind of Monster (139 minutes, at area theaters) is rated R for profanity and brief nudity.

"Some Kind of Monster" follows James Hetfield and his Metallica band mates through some trying times.