When Joaquin Phoenix announced that he was retiring from acting in the fall of 2008, and months later, looking disheveled and disoriented, made a disastrous appearance on "The Late Show with David Letterman" to promote his last movie, 2009's "Two Lovers," the media and public at large suspected the whole thing was a hoax. Fellow actor and brother-in-law Casey Affleck denied these assumptions, saying that he was directing a documentary about Joaquin's attempt to become a hip-hop artist. The resulting film is "I'm Still Here," but it is not so much a "making-it-in-the-music-biz" tale—based on the music we hear here, Phoenix won't be "making it" anytime soon—but a shattering look at a celebrity's complete public and mental meltdown. Having seen it, there are still many questions about whether or not what has been captured by Affleck's camera is authentic or an elaborate con, performance art taken to the limit. If it's the former, then it's beyond tragic. If it's the latter, then Phoenix deserves every acting award that could possibly be heaped upon him. Either way, giving the movie a star rating seems rather arbitrary. As a piece of cinema, the experience is alternately fascinating, terrifying, maddening, self-indulgent, amusing, worrisome and insufferable. Kind of like Phoenix's persona.

There is no denying that Joaquin Phoenix is a major acting talent who has delivered outstanding performances in such films as 1995's "To Die For," 1999's "8mm," 2000's "Gladiator," 2002's "Signs," and 2005's "Walk the Line." "I'm Still Here" wants us to believe that he is now tired of the profession and ashamed at the choices he's made in his career. He wants a change. Maybe this is so, but if the film is at all truthful, Phoenix's problems run much deeper to a place that director Casey Affleck is unwilling to go. Increasingly scruffy and unkempt, slurring and incoherent, chain-smoking while constantly wearing a germ mask around his neck or on top of his head like a fashion accessory, Phoenix has flown right off the deep end. Even if the viewer is to disregard his recreational drug use, made all the more upsetting because we remember very well what became of his older brother River in 1993, the subject is in desperate need of help, yet has no one who cares about him enough to do anything about it. With most of Phoenix's acquaintances on his payroll and no true friends, Casey Affleck irresponsibly turns his camera on and observes a man who is self-destructive and self-destructing, making a mockery of himself, and undone further by his own infuriating ego. Beyond self-involved, Phoenix spends the majority of his time abusing and belittling his assistant Antony Langdon, childishly whining about how hard life is for him, pouting when he doesn't get his way, and generally obsessing over himself without giving anyone else another thought. On this last point, at least it goes both ways.

"I'm Still Here" would be very funny if it weren't so depressing. Inflated by his own skewed sense of fame and what it can do for him, Joaquin believes that all he has to do is announce he is becoming a hip-hop musician and it will magically happen. His few stage performances are embarrassments and his meeting with Sean Combs is uncomfortable in the most watchable of ways as the mogul tries to go easy on Phoenix even as he can't believe what he hears on the demo CD. A meeting with Ben Stiller, who wants Phoenix to be his co-star in the film "Greenberg," is rife with slights and put-downs at the expense of Stiller's comedy career, adding hilarious newfound context when we later see Stiller on an awards show dressed as Phoenix and making fun of him while co-presenter Natalie Portman comments that he looks like he should be running a Hasidic meth lab. A later scene where Phoenix verbally assaults Antony and his assistant gets him back by defecating on his face is just plain gross, a mirror of how pathetic they both are. The only time where Phoenix becomes the least bit sympathetic is in a raw moment following his near-apocalyptic appearance on "The Late Show with David Letterman" where he has a catharsis about how far he's fallen and how much work he'll have to do to ever be taken seriously again. In this scene, the viewer understands that he's more than just a victim of his own choices, but of an entire Hollywood culture that chews up and spits out the weak and vulnerable.

While there is a certain level of artifice to "I'm Still Here," it is only in the logistics of Casey Affleck being allowed to make something so professionally damning of Joaquin Phoenix. Shouldn't Affleck's wife, Summer Phoenix (who never appears), have had her own qualms about what he was doing? This is never brought up. If, in a few months' time, Affleck and Phoenix finally come clean and laugh about pulling one over on everyone, then that would be the happiest of endings for Joaquin. Timed just right, such an announcement would be enough to earn him a well-deserved Oscar nomination and likely a win. If, however, this really is more documentary than mockumentary, well, then the whole thing is rather sad, far too reminiscent of Gus Van Sant's harrowing 2005 drama "Last Days" for comfort. A psychological snuff film, "I'm Still Here" is unpleasant and provocative in equal measure. You don't necessarily like what you see, but it's impossible to turn away from the carnage.