Here's why Rouben Mamoulian's Blood and Sand is the highlight of that Tyrone Power collection.
Mamoulian's work at Fox was very impressive, but like a lot of great directors who signed with Fox in the '40s (Lubitsch, Sturges), he started out strong and then ran into conflicts with Zanuck and a lot of canceled projects. In Mamoulian's case, he was fired from a number of Fox pictures, most famously Laura where he was replaced by the film's producer, Otto Preminger. By the late '40s, despite his enormous success as the director of the original Broadway productions of Oklahoma! and Carousel, he'd become almost unemployable in Hollywood; he completed only two more pictures, both for Arthur Freed (Summer Holiday, an underrated musical with Mickey Rooney, and Silk Stockings, which is a good movie but hardly looks like a Mamoulian picture at all). He was also fired off a number of big-budget films like Porgy and Bess and Cleopatra.
It's too bad that Mamoulian didn't get to make many film musicals after the '30s; his black-and-white musical Love Me Tonight is deservedly considered one of the classics, but as you can see from the clip above, he would have done an amazing job if he had been let loose on a Fox Technicolor musical -- imagine his instinct for combining color, music and movement, spread throughout a whole film.
The ideal thing, of course, would have been for Mamoulian to have directed the film versions of Oklahoma! or Carousel. The actual film versions are very dreary and stolid-looking; they really needed the Mamoulian touch.