On one level, it's a sort of prank. Director Spike Jonze was the guy who directed a Weezer music video ("Buddy Holly") by dropping the band into a Happy Days rerun, who hired dancers to dress like chumps and impede the human traffic flow in front of the Mann Westwood Village theater for Fatboy Slim's "Praise You." For his feature film debut, he's made a movie about a hidden doorway that leads you into the head of John Malkovich, lets you stay there for exactly 15 minutes (the Warholian duration of fame) and then spits you out, roughly, on the shoulder of the New Jersey Turnpike.

But on another level, it's a sober meditation on loneliness and disenfranchisement (consider David Fincher's Fight Club a distant sibling), and the feeling of wanting to slip into someone else's skin, either for a few minutes or for a lifetime.

An atypically unkempt John Cusack stars as a talented puppeteer who needs a job. He's resigned to the fact that his skill set isn't exactly in high demand, but those nimble fingers are at least good for filing paperwork, securing him work with an obscure company in low-ceilinged quarters crammed between the 7th and 8th floors of a Manhattan office building -- the casual lunacy of these scenes recalls a Monty Python sketch. His wife is a frizzy-haired Cameron Diaz, an animal-lover who thinks she may want children, too.

The film's main catalyst isn't so much the Malkovich portal as it is the caustically sexy co-worker (a terrific Catherine Keener) who catches Cusack's wandering eye. Her interest in him is akin to that of a cat playing distractedly with a mouse it really has no plans to devour. But, once alerted to the existence of a backroom passage into Malkovich's brain at the office, it's she who figures on making a bundle by charging admission after hours.

And it goes from there. Despite telegraphing the final punchline several reels in advance, Being John Malkovich unfolds as an intellectual funhouse ride -- there's a new surprise waiting around every corner. That the film's chosen fetish object is a semi-famous personality like Malkovich shows how precariously its universe balances between a pleasantly skewed reality and utter dementia. In a meta-cinematic sense, the real fascination on offer is Malkovich himself doing a wry impersonation of John Malkovich, and then impersonating John Malkovich being inhabited by other people. He turns in a fine comic performance -- isn't it a little ironic that, in some ways, it's his best to date?

If this is really a movie about acting, the key metaphor is puppetry. The two quasi-antagonistic leads are driven by a variety of megalomania, a desire to control. This interest manifests itself both sexually, as the characters learn that being John Malkovich (and being with John Malkovich) can be a huge turn-on, and professionally, as it becomes apparent that Malkovich's actions are significant not because of the inherent worth of what he's doing, but because it's Malkovich who's doing it. Scheming ensues.

The rate of mad invention flags a little in the second half, as rote exposition takes over and the comedy is yoked to the insane demands of managing to move a story this out-of-control toward something resembling a resolution. But in the annals of great left-field ideas that moved to the screen without being decimated by the studio development process, marketing departments, or test audiences, this one should loom large. The excitement of watching Being John Malkovich comes from the realization that the weirdness coheres, that the movie has something real to say about the conditions we place on our own happiness and the genuinely weird demands we make of others.