Double Wedding is a romp. Its set-up is close to that of Moonlighting: rich, glamorous, control-freak woman meets brash, odd-ball man who shakes up her neat world. Shepard's character was a model, Loy's designs and retails fashion; Powell's character is an artist, Willis's character is a detective and a dreamer, a con-man, a fantasist... Chemistry ensues.
Both the TV show and the film are charming.
Double Wedding film still borrowed from Immortal Ephemera
My favorite of the Loy/Powell films is probably still The Thin Man and its sequels - just sooo '30s sophisticated and funny - with Love Crazy in second place. Double Wedding is interesting mostly because Powell plays a Bohemian, rather than his usual man-about-town. Frankly, I'll take Loy or Powell in any movie, by themselves, but best of all together.
(The website Immortal Ephemera has a good summary of Double Wedding with more movie stills.)