When “Dreamgirls” debuted on Broadway in 1981, it was Jennifer Holliday in the show-stopping, second-string role of Effie White who brought down the house and became a star rather than lead actress Sheryl Lee Ralph. Now it’s happening all over again in Bill Condon’s film adaptation of “Dreamgirls,” with “American Idol” reject Jennifer Hudson in the Effie role and multi-platinum recording artist Beyoncé Knowles as the ostensible lead, Deena. Critics are giving Ms. Hudson breathless endorsements (“mellifluous,” “blazing,” “sensational”) and, even better than an Oscar, she received a congratulatory phone call from Oprah Winfrey. As for Ms. Knowles …well, if you can’t say anything nice you shouldn’t say anything at all, and no one’s saying anything at all about her performance, so let’s just assume they’re being nice.

It’s not a fair contest. If you’re looking for resonance, then Effie White resonates like a cathedral bell. The character is based on Florence Ballard, the founder of the original Supremes, who was widely considered the most talented in the group but was bumped from the lead microphone in favor of the lighter and whiter Diana Ross. A few years of humiliation later she was fired for being either a) too drunk, b) too fat, c) too difficult, or d) all of the above. Originally, Ballard’s role was to be the second-banana part in “Dreamgirls,” but Ms. Holliday fought like a fury to have it rewritten, and by the time she was finished, Effie White was the backbone of the show, Ms. Holliday’s performance received more awards than she could polish, and her signature number, “And I’m Telling You I’m Not Going,” hit no. 1 on the R&B charts.

When Ms. Hudson was voted off the third installment of “American Idol,” guest judge Elton John called it “racism” and a lot of people agreed, and so her role in “Dreamgirls” — focused as it is on her character getting passed over for the nicer, lighter Deena, who represents the band’s chance of crossing over to the white mainstream — carries a charge of pop culture frisson. But for all the praise she’s garnered, Ms. Hudson ain’t no Jennifer Holliday. On the other hand, she ain’t no Beyoncé Knowles, either. Where Ms. Knowles brings all the gritty realism of a pampered pussycat who sleeps on pashmina and drinks hand-churned cream, Ms. Hudson brings realness. She’s short and stocky, she’s a mouth-breather, she’s dark-skinned, her hair is kinky, and her upper arms look like a real woman’s upper arms instead of sleek, gym-toned, muscular.

The movie, a fictionalized account of the rise of the Motown sound with the Dreamettes standing in for the Supremes, has been hailed as the second coming of cinema, but from where I was sitting there were only two things worth looking at, and one was Ms. Hudson. Surprisingly, the other was Eddie Murphy as a James Brown stand-in, James “Thunder” Early, whose lady-slaying roadshow has made him king of the chitlin circuit. Early can’t cross over to the mainstream because his pelvis pumping makes white ladies blush and white men wither, so his star tumbles as Deena’s rises.

For once, Mr. Murphy drops his shuck-and-jive shtick to deliver a real performance, and while the realness part is beyond him, he’s a hell of a performer. His verbal patter is as lethal and unrelenting as a machine gun and he carries himself like most great stage performers, all of whom hide a shameful secret: The only person they want to make love to is themselves. Since that’s physically impossible, they stand onstage and explode in white-hot supernovas of sexuality and self-destruction. Late in the movie, when Mr. Murphy drops his grin, relaxes his face, and actually listens to someone else for a change, it’s one of the most affecting moments in the film.

With four new songs shoehorned in, including an 11 o’clock number that tries to shift the focus back to Ms. Knowles, “Dreamgirls” lasts about as long as Diana Ross’s career. Like Ms. Ross, by the time it drags itself over the finish line, it looks like a worn-out drag queen, and you can’t remember why you ever enjoyed it in the first place. It’s a camp desert with Ms. Hudson and Mr. Murphy’s numbers scattered across it like little oases. The story is already pretty slight, the awkward attempts to inject social relevance (cue the Detroit riots!) are more laughable than sobering, and the editing is unforgivable. In the middle of “And I’m Telling You I’m Not Going,” the editor decides that just as Ms. Hudson hits one of the higher, more dramatic notes, he should cut away to Jamie Foxx.

“Dreamgirls” was a smart musical — it had something to say, it said it, and though it did some preaching, it knew how to keep the audience entertained. That’s why it ran for more than 1,500 performances and became a Broadway legend. But there’s a hollowness at the center of the “Dreamgirls” movie that all the sequins and production design in the world can’t hide.

It makes the same points as the musical not because the director passionately believes in them but because he’s crafting a product called “Dreamgirls” and those are the points “Dreamgirls” made in 1981, so they’re the same points it will make in 2006. The period design is bland and the costuming is merely efficient. Even Ms. Hudson’s show-stopping numbers are, apparently, a carbon copy of how Ms. Holliday performed them, right down to her costumes.

“Dreamgirls” simply has no soul — it’s cinematic karaoke. And it’s an irony that will be lost on no one that a movie about how Motown bleached the color out of its artists to make them more acceptable to a white audience has bleached all the color out of its story to make it more acceptable to a mainstream audience. In all likelihood it’ll break the $100 million barrier at the box office and win an Oscar, but a year from now no one will remember what all the fuss was about.