Well, here's a fresh twist on an enduring genre: a lavish big-screen movie musical, based on the charming, long-running Broadway show, in which very few of the actors can hold a note. But hey, if you have the misfortune of living in a world where people regularly break into song, what else can you do but give it the old college try? With an infectious playlist exclusively taken from the hits of pop group ABBA, "Mamma Mia!" spins a lightweight plot around the centerpiece production numbers and has a lot of fun doing it. The film, it should be said, doesn't hold a candle to the stage musical, nor do the A-list stars in the ensemble, who were clearly picked for name value rather than singing talent. There is a fine line between something that is so bad it's good, and something that's genuinely good, and "Mamma Mia!" straddles it throughout.

For all of her life, 20-year-old Sophie Sheridan (Amanda Seyfried) has lived with single mother Donna (Meryl Streep), lending a helping hand with the Greek villa she owns. With her wedding to Sky (Dominic Cooper) fast approaching, Sophie stumbles upon her mom's old diary and comes to the conclusion that any one of three guys—American architect Sam Carmichael (Pierce Brosnan), British banker Harry Bright (Colin Firth) and Swedish adventurer Bill Anderson (Stellan Skarsgård)—could be her father. She secretly sends out invitations to them and, to her surprise, they all show up. As Donna reconnects with old friends Rosie (Julie Walters) and Tanya (Christine Baranski), the trio of them a former music group known as Donna and the Dynamos, she is also suddenly faced with three lovers from her past that she never expected to see again. Donna, too, isn't sure which one is Sophie's real dad.

Theater director Phyllida Lloyd, making her feature debut, probably wasn't the wisest choice to helm "Mamma Mia!" At least at the onset, she instructs her actors to perform broadly and as if they were on a stage, with a lot of running, squealing and manic arm-waving. She also seems confused half the time where to point her camera. Editing is rough around the edges and choreography is hurt by too much cutting in lieu of allowing the scenes to breathe and play out unobtrusively. Some of her cinematic flourishes are also misguided, with "Money, Money, Money" approached as a fantasy sequence where Donna is a wealthy, highfalutin madam with a luxurious yacht and endless cash at her disposal. Say what?

Performances are brave even when the actors are miscast, but their lack of vocal training does not exactly help matters. The best of the bunch is Amanda Seyfried (2004's "Mean Girls"), whose lovely voice and wide-eyed appearance helps to make Sophie a sympathetic presence. As Donna, Meryl Streep (2007's "Lions for Lambs") looks to be having a ball, but her wobbly turn is not up to the level one has come to expect from her. She has a few beautiful numbers—"Slipping Through My Fingers" is a touching ballad that bridges a much-needed mother-daughter connection with Sophie; "Dancing Queen" is a boundlessly energetic showstopper where the whole of the island joins in as back-up; and "The Winner Takes It All" is a slow-burner that concludes stunningly—but often appears to be having trouble keeping up with the music.

Julie Walters (2007's "Harry Potter and the Order of the Phoenix") and Christine Baranski (2004's "Welcome to Mooseport") lap it up as comic relief Rosie and Tanya, but also aren't always assured in their singing. The same goes for Stellan Skarsgård (2004's "Exorcist: The Beginning") and Colin Firth (2005's "Nanny McPhee") as affable possible fathers Bill and Harry, though Firth does do a nice, low-key job with "Our Last Summer," over which he bonds with Sophie. Save for their sexy duet, "Lay All Your Love on Me," Seyfried and Dominic Cooper (2001's "From Hell"), as Sky, lack the chemistry they should have. Cooper gives off the impression of an oily bohunk rather than a nice guy. And then there's Pierce Brosnan (2005's "The Matador") as Donna's central love interest Sam. With all due respect to the handsome and charismatic Brosnan, he's an awful singer who should never warble outside of his shower stall. Whenever he opens his mouth with a song, it inspires unwanted laughs and ruins at least one would-be magical set-piece set to the tune "SOS."

"Mamma Mia!" will not be going down in the history books as a wholly successful musical, but for fans of ABBA not even Brosnan's butchering of their albums is enough to put the kibosh on the picture's winning entertainment value. The story, as thin as it is, finds its footing in the second half and finishes with a few surprises and a lovely, upbeat denouement. The location lensing in the Greek Islands is attractive and picturesque, as well, opening up the proceedings enough so that it doesn't feel quite as stagy as it is. "Mamma Mia!" is frothy and virtually painless. It's toe-tapping fun while it lasts, and then evaporates as quick as it comes.