In the best of Robert Altman's ensemble pictures, his sprawling casts fall into a sort of miraculous rhythm. No matter how divergent their storylines might be, there's never a sense that actors aren't on the same page. In MASH, for example, not only are Donald Sutherland's Hawkeye and Elliot Gould's Trapper John completely in sync, but they also share a clear understanding with Sally Kellerman (Hot Lips) and Robert Duvall (Frank Burns). And in The Player, no matter how reptilian and icy Tim Robbins' Griffin Mill gets, he never fails to share convincing connections with every other major actor in the film -- despite its rangy story, never once does the movie feel like anything less than a coherent whole. By the same token, however, when things go wrong for Altman they go very, very wrong. Despite its world-class cast, Prêt-à-Porter is a sprawling mess, full of characters and performances that have nothing to do with one another, and a story that exists simply to give them all an excuse to be in the same movie.

While Altman's latest feature, A Prairie Home Companion, is by no means the aggressive disaster Prêt-à-Porter was, there nevertheless is something off about. Stocked with an all-star cast that includes Meryl Streep, Kevin Kline, John C. Reilly, Lily Tomlin, Lindsay Lohan, and Tommy Lee Jones, the movie never congeals into a coherent whole, despite a handful of heart-felt performances. Set backstage at an old-time-style radio show called A Prairie Home Companion (also the name of screenwriter-star Garrison Keillor's long-running show on NPR), the movie takes place during the show's final performance: The Fitzgerald Theater in which it is based has been bought out, and the new owners have no interest in hosting a radio show. As Altman is wont to do, he jumps back and forth among stories that include a pregnant stage manager (Maya Rudolph), lovers planning a tryst (L.Q. Jones and Marylouise Burke), an angel (Virginia Madsen) in search of a soul, singing sisters reminiscing about their careers (Streep and Tomlin), and a star uncomfortable with saying goodbye (Keillor). Though the disparate storylines are all somewhat interesting in their own rights, the characters within them never become human enough for the audience to get engaged in their lives. Surprisingly, this is even true for Streep, one of the most accomplished actresses of her generation, and Tomlin. Instead of slipping into the easy rhythm Altman clearly wants from them, the actresses instead languish in a sort of surface jocularity made up mostly of cliched memories and missed emotional connections. It's disappointing to see the two of the flounder so, and the movie as a whole often seems to be suffering the same fate.

In the role of Guy Noir, Kevin Kline seems to be in an entirely different movie than the rest of the cast. In some ways, the awkwardness is understandable: He's playing a character from Keillor's radio show -- a silver-tongued 1940s-style private eye who speaks in nothing by similes -- as a real person, and that real person has nothing to do with the modern world in which the movie is set. In addition, Kline's periodic forays into physical comedy, while funny, do nothing more than isolate him further from the rest of the cast. Similarly distant is Virgin Madsen's angel, a unnecessary character to whom she gives a preposterous, off-putting aloofness. Drifting through the movie in a tightly-bound white trench coat, Madsen's angel is cliched to a degree that is beneath Altman, and the character further mars the movie's already flagging rhythm.

What ultimately makes A Prairie Home Companion disappointing, though, is how close it comes to being really good. There is some fine acting in the movie, and the actual radio show sequences are truly magical. Streep and Tomlin, Woody Harrelson and Reilly, Lohan, and Keillor all take their turns singing before the movie's studio audience, and the performances are uniformly good; together, they're easily the best thing in the film. Streep's character in particular comes to life when she's behind the microphone, unleashing all of the convincing passion and spontaneity that are lacking from the rest of her work in the movie. And both behind the mic and away from it, Harrelson gives what is surely one of the best performances of his career. Like Kline, he and Reilly play radio show characters come to life -- Dusty and Lefty respectively, cowboys long on the trail who tell bad jokes and sing from time to time -- but they do so with such genuine warmth and affection that their inappropriateness to the real-world surroundings never becomes an issue. Harrelson in particular is impossibly winning, infusing Dusty with such cheeky good humor and cheerful unpredictability that the character becomes utterly irresistible.

Also impressive, surprisingly, is Keillor, a man who has spent his entire career behind a radio mic. Exhibiting none of the awkward stiffness you might expect from a neophyte dealing with Altman's improvisation style, Keillor instead turns in one of the movie's most natural performances. Perhaps because he's essentially playing himself, he comes across as open and completely without pretense, qualities that are particularly refreshing given how false some of the film's interactions ring. Additionally, in a tiny role as a representative of the Fitzgerald Theater's new owners, Tommy Lee Jones once again proves that he's never met a movie he couldn't make better. In just a few minutes on screen, Jones infuses the movie with a profundity and pathos that it had been missing, despite the cast and director's most fervent efforts. Almost single-handedly, he pulls the film together and, for a few moments, makes us care about what happens to its characters.

To a fan of both Altman and Keillor's radio show, the failures of A Prairie Home Companion are doubly disappointing and, while the movie is far from the director's worst, its frequent stumbles are impossible to overlook. At best, the film is Altman-lite -- better, perhaps, than a lot of its competition, but in no way representative of the legend's true powers.