Besides the aerodynamic shape, the distinct features such as all-enclosed fenders, the accent dash that runs from the grille, over the hood and hugs the rear fender, four fully hidden front lights. To break up the side skirts, a belt line runs along the fenders that makes the car look bulbous but doesn't subtract from the overall elegance.
Unique features of the interior include a plush ostrich skin uphostery, a sliding metal sunroof and a front windshield that can wind open for ventilation. I particularly love the door handle design, and the repetitive curve design that is the overall shape, the fender leading edges, the chrome accents on the fender skirts, the chrome accents on the side grills down the sides of the hood.
Inspired by http://info.detnews.com/joyrides/story/index.cfm?id=261 images and info from http://www.supercars.net/cars/1939.html