Perhaps the greatest exploitation film of all time, Browning's early-sound-period masterpiece tells the story of the titular freaks, who travel around with the circus for the entertainment of "normal" people. Rather than holding them up to scorn, Browning focuses on how they have formed a family, manifested in their revenge against a gold-digging trapeze artist. By extension, Browning is examining the tendency of all those outside mainstream society, "the unwanted" as they are called in the opening crawl, to band together against the world that has rejected them. There is, of course, the obligatory romantic subplot between the "normal" characters, but that's less interesting than the film's observation of its various genetic misfits, like the legless Johnny Eck, who ambles around on his hands, and the limbless Prince Randian, who lights a cigarette using only his mouth. When the final revenge scene comes, Browning wisely avoids showing the scene in great detail, instead concentrating on shadows and nightmarish imagery.
See also: The Movie Moment: Freaks (Screengrab)