“Simone” demonstrates that a one-joke movie can work just fine if the joke’s a good one and is well delivered. The premise of Andrew Niccol’s sophomore feature is that a washed-up Hollywood director completes his latest picture by stealthily inserting a computer-generated “actress” into the lead role when his pampered, egomaniacal star walks off the project; the simulated performer immediately becomes a sensation, reviving the helmer’s career but forcing him to go to great lengths to keep the public from learning that their new idol is a fake. In time, of course, the stress of the deception leads the poor guy to take increasingly desperate measures to rid himself of his own superstar creation.

“Simone” shares with the script that Niccol penned for “The Truman Show” (and with his first directorial effort “Gattaca”) an underlying interest in issues of identity and reality, and, like “Truman,” it makes satirical points about modern notions of celebrity, but it treats these matters more lightheartedly; and though the underlying theme is equally thin, it holds up better here than in either of his earlier efforts, both because the less serious tone minimizes the sense of false profundity from which they suffered and because Al Pacino is around to give an utterly virtuoso performance as would-be auteur Viktor Taransky, the Svengali of the titular headliner (her name is a compression, we’re told, of “Simulation One”). Looking perpetually haggard and exhausted, Pacino plays the part at lower voltage than usual, but the electricity is always perceptible; and he has some inspired moments when he converses with the computer-generated Simone, whose voice he provides himself. It’s about as wickedly knowing a portrait of a crazed, self-absorbed director as Dustin Hoffman provided of a similarly afflicted producer in “Wag the Dog” (1997); the two turns are delightfully complementary. (And in the present case the humor is heightened by the fact that Niccol–also a writer-director-producer who makes big but “arty” films in a style very much his own–is having some fun at his own expense, too.)

There are other strengths in “Simone.” Winona Ryder, of all people, is uncannily sharp as the star who tries to sabotage Taransky’s picture and afterward approaches the revivified director with profuse apologies for her bad behavior, and Evan Rachel Wood is brisk and likable as the helmer’s computer-savvy daughter. On the male side, Elias Koteas (unbilled, it appears) provides an amusing cameo as the wacked-out inventor of the Simone program who entrusts it to Viktor, while Jay Mohr gets some laughs as an understandably insecure leading man. As with “Gattaca,” Niccol has assembled a design team–designer Jan Roelfs, art director Sarah Knowles, set designer Randall Wilkins–that’s given the picture a stylishly spare, modern look, and Edward Lachman’s cinematography has wonderful crispness and sheen. In Simone, moreover, the film offers the best computer in a supporting role since HAL-9000 stole his scenes in “2001.” The credits are cagey about the nature of the character, implying that’s she’s actually a special-effects construct rather than a flesh-and-blood actress. That’s hooey–an pretty young thing named Rachel Roberts is directly involved–but the effects team deserves the highest kudos anyway, and the misleading info is a conceit that’s permissible as a device to extend the central joke past the final crawls.

Unfortunately, there are weaknesses in the picture as well. Catherine Keener doesn’t do much with the role of the studio honcho who’s Taransky’s ex-wife (shades of “Hollywood Ending”), and while Pruitt Taylor Vince and Jason Schwartzman work well together as a couple of tabloid reporters out to uncover the truth about Simone, some of Vince’s material, involving his character’s sexual obsession with his quarry, gets a bit too creepy to be entirely funny. More seriously, several aspects of Niccol’s script are miscalculated. The most obvious involves the clips we see from Taransky’s movies (including one he pretends that Simone has directed): the titles (“Sunrise, Sunset,” “Eternity Forever,” “I Am Pig”) are laughably pretentious, and all the scenes are take-offs on sixties “art” films, showcasing phonily meaningful images and dopily “philosophical” dialogue. These gags aren’t bad in themselves, but they make it impossible to believe that the pictures could ever achieve the sort of popular success they’re supposed to; the mass audience would never pay money to see such stuff, no matter who might star in it, and that eliminates the shred of credibility we need for the conceit to be fully sustained. (They seem, in fact, like heightened versions of Niccol’s own work, when it would have been more persuasive had they looked like something made by Michael Bay.) A similar problem afflicts Viktor’s third- act attempts to turn the public against Simone: at one point he has her appear on television in a state that would necessarily turn off virtually everybody, but Niccol wants us to believe it only increases her popularity, and the extreme implausibility undermines the effect. Finally, there’s the last act. The turn the plot takes is telegraphed too soon, and resolved with ridiculous ease. It does give Pacino some very funny lines, though.

Still, “Simone” works more often than not, and in Pacino it has an authentic star with the chops to propel it over the rough spots. Even with its flaws, the picture remains a delicious takeoff on the culture of celebrity and the Hollywood studio mentality. Viewers with a taste for insider humor should find it a special treat.