In a perfect world, every good movie would have a really good screenplay, but there are films like Sun Valley Serenade that are totally winning in spite of the fact that their script is really nothing more than serviceable. This kind of situation occurs more often with musicals than with films from other genres, because the songs, dances and spectacle play such a big part in our enjoyment of them. While Serenade's script is professional and on sports a number of amusing lines and situations, it's mostly a situation of getting from A to B to C -- and of finding a way to set up the musical and ice skating numbers on the way. Oh, and of showing off the gorgeous scenery of Sun Valley and of displaying the glories of skiing and skating that can be had there. It really shouldn't work as well as it does, but with Sonja Henie on hand to dazzle with her glacial terpsichore (including a marvelous black ice routine) and Glenn Miller and his boys around to swing through "Chattanooga Choo Choo," "In the Mood" and "Moonlight Serenade," the entertainment factor is just too high to resist. Throw in a lovely young Dorothy Dandridge for some too-brief vocalizing, some really nifty dancing from the Nicholas Brothers, and comedy bits from Milton Berle and Joan Davis, and Serenade emerges a real winner.