MGM head Louis B. Mayer didn't want Myrna Loy in the part of Nora Charles. Also, the studio needed her in three weeks for another movie. Director W.S. Van Dyke had worked with Loy and William Powell in another movie, and wanted them to play Nick and Nora. Van Dyke had a nickname around town, "One-Take Woody". He had no problem bringing pictures in on time. There is some disagreement on how long it took Van Dyke to shoot The Thin Man ... some say 16 days, others say 18. One thing everyone agrees on is that he was done before the three weeks were up.
You can feel this in the breeziness with which the picture goes by, and Powell and Loy deserve a lot of the credit. Their interplay as a happily married, often drunk couple had not been seen before. They made marriage sexy. They were doing something right ... The Thin Man was such a success, it spawned five sequels with the stars. It was nominated for 4 Oscars.
Roger Ebert noted that the relationship between Nick and Nora was like that of Fred and Ginger in their musicals. "The movie is based on a novel by Dashiell Hammett, one of the fathers of noir, and it does technically provide clues, suspects and a solution to a series of murders, but in tone and intent it's more like an all-dialogue version of an Astaire and Rogers musical, with elegant people in luxury hotel penthouses and no hint of the Depression anywhere in sight." It was the film of Raymond Chandler's The Big Sleep that famously lost track of who killed who, but long before that, The Thin Man showed that no one cared who did it when the stars were so much fun to watch.
In fact, despite its reputation, The Thin Man drags through much of its beginning, basically until Powell and Loy turn up. And the big reveal, which takes place at a dinner party, is endless ... the only good parts are the occasional wisecracks, as Nick Charles explains who done it. None of this matters when Nick and Nora are drinking and being in love. If it all seems a bit familiar now, it's only because it set a standard that has been copied many times over since then. Also with Maureen O'Sullivan and Cesar Romero.