Sure, it’s nice that the actors sing their own numbers—Meryl Streep has a fab set of pipes, and the fact that Pierce Brosnan sings like a bullfrog in heat is used to adorable effect. But without the originals’ multiply dubbed wall of sound, these ABBA tunes only get their due in the all-too-rare big production numbers, when Mamma Mia! finally rocks as a tirelessly nostalgic pub crawl through a narrow street of 1970s pop history. Otherwise, it’s little more than droopy ditties draped around a threadbare plot about the daughter (Amanda Seyfried) of a single mom (Streep) who secretly invites three men in a boat (Brosnan, Colin Firth, Stellan Skarsgård)—each of whom might be her father—to her Greek island wedding. For all its half-hearted stabs at catering to the transatlantic youth market, Mamma Mia! is a (Shirley) valentine to 50-something, we’re-not-done-yet broads, three of whom—director Phyllida Lloyd, screenwriter Catherine Johnson, and co-producer Judy Craymer—successfully courted that underserved demo in the hit stage version, but haven’t a clue how to make a movie. A mugging Streep is eclipsed by Christine Baranski, stealing the show in a coyly filthy dance number with a corps of pectorally gifted young blades. In moments like these, Mamma Mia! takes enchanting ownership of what it is: a stage musical that made a big ol’ heap of money, shoved onto the big screen to make a whole lot more.