The first ten minutes or so of Dreamgirls explode with energy: Set during a talent show in early '60s Detroit, it showcases one powerful African American performer after another, belting out strong, intense, and unapologetically Black music. A trio of teenage girls calling themselves The Dreamettes squeak onstage at the last minute and wind up bringing the house down. In the shadows lurks a Cadillac salesman named Curtis Taylor Jr. (Jamie Foxx), whose solemnity barely masks his oiliness. Quickly he becomes manager for the Dreamettes, getting them a job singing backup for a James Brown-like singer named James "Thunder" Early (Eddie Murphy) and eventually driving them to stardom as The Supremes. Er, I mean The Dreams.

It's well-known that Dreamgirls is based on the true story of The Supremes and Motown founder Berry Gordy Jr.; when it originally opened on Broadway in 1981, however, the bit of pop music history that it covers was so recent that the show's producers and writers futzed with enough story details to make sure neither Gordy nor Supremes frontwoman Diana Ross could sue them.

With an extra quarter-century of distance, however, writer/director Bill Condon, who adapted the hit musical for the screen, makes some smart decisions in bringing the story closer to the reality on which it was based. And so Curtis hails from Detroit, home of Gordy, instead of the stage's New York; Curtis's Rainbow Records is more closely modeled on Motown (complete with an ersatz Jackson 5); and light-skinned Beyoncé Knowles is cast as Deena Jones, the Diana Ross stand-in, whereas the show's Broadway director Michael Bennett had insisted on the dark-skinned Sheryl Lee Ralph. These are not just surface changes: they strengthen Dreamgirls' relevance as a film, which is beneficial, given the dated theatricality of its source material.

That said, my brain and my gut had different reactions to the film. On an intellectual level, I cannot fault anything about it. Yes, it's too long, and the ending is corny, but blame the Broadway show for that. And yes, many of the songs are sappy, a couple of them downright insipid. But I think that's part of the point: The story is about Effie White (a revelatory Jennifer Hudson), the loud, chubby lead singer for The Dreamettes who is eventually relegated to the background by the ruthlessly ambitious Curtis - her lover, no less - as he seeks to ingratiate the group to a wider (read: white) audience by placing the bland but beautiful Deena in the lead. (Effie is based on Florence Ballard, the doomed founder of The Supremes.) So while Effie's - and Jimmy Early's - numbers shimmer with the gospel-tinged rawness of black music, the songs that the other characters croon are syrupy and mundane, reflecting the white bread world that they aspire to. It's clever, but you still have to sit through some pretty cheesy songs.

At least Condon, who knows that the rules of old-fashioned Hollywood musicals won't fly with contemporary audiences, finds a way around the goofiness of people breaking into song by shooting each number on stage or in a recording studio, so that even as the characters sing to each other, it is still in the context of their milieu. But even though the songs advance the story, as good musical numbers are supposed to, they frequently fizzle onscreen. There's a reason why the only two really great movie musicals over the last four decades - Chicago and Cabaret - are both Kander and Ebb shows: These two songwriters chose to mimic the music of the eras their stories were set in, so the films worked as period pieces. Dreamgirls (music and lyrics by Henry Krieger and Tom Eyen) almost succeeds as a time capsule of the '60s and '70s pop world, but the songs themselves lack the authenticity.

Still, no matter what you might think of the film, you can't deny that it gets ten times better whenever Jennifer Hudson is on screen, and especially when she sings. She's downright amazing, and the irony of her being cast in the role of the hapless Effie (as Hudson was a hit on American Idol but similarly lost the competition to Fantasia Barrino) only enriches her performance.

Eddie Murphy is quite good too, and there's some poignancy to seeing the once-hot superstar, whose recent screen career has been an embarrassment, play a man fighting to stay relevant in changing times. Beyoncé Knowles is appropriately bland, and Jamie Foxx, who seems a bit stiff at times, personifies the soullessness - in all senses of the word - of Berry Gordy, whose Motown may have created a string of hits that most of America now finds nostalgic, but who, as Dreamgirls would have you believe, sucked the very essence out of black music while making it palatable to the white majority. Despite the feel-goodness of the film, it's a bitter sentiment, and Dreamgirls is a poison pen letter to Gordy's empire.