Widely considered the best Marx brothers film ever (and landing at #5 on the AFI's list of top comedies), Duck Soup presents Groucho at his best, playing a dictator (of a country called Freedonia, natch) who starts a war over a girl who lives in a neighboring country (and who has saved Freedonia from bankruptcy). The other brothers Marx play the dictator's henchmen and spies. It's a farce about politics and war that, in my opinion, has lost some of its topicality. While the puns here are exquisitie and Groucho sparring with himself in a mirror (actually a stand-in) is a priceless moment of the cinema, the send-up of Mussolini-types doesn't quite pan out. Take the comedy, leave the story.
The Marx brothers are on top of their game here with a horse-race oriented gagfest (Groucho is a veterinarian mistaken for a human doctor)... at least when the film isn't detoured into an extended musical ballet number or endless sing-song bit. Maureen O'Sullivan's appearance is a bit expendable, but the bits the brothers schtick through are often just priceless. One of the Marx brothers' best.