Snapchat consistently ranks highly in the App store. I also hear designers consistently ridicule it for being ugly and unpolished.
I believe Snapchat benefits from its lack of polish. The roughness of the interface encourages sharing rougher (and lewder) moments of life. Your 5-second kegstand video belongs on Snapchat. It doesn’t belong in a pixel-perfect ‘just so’ interface.
An interface frames its content and dictates what’s appropriate. Over-polished UI adds a degree of self-consciousness to sharing. Blurry photos of people riding mechanical bulls don’t belong in art museums. But they might belong on the wall of a dive bar.
Beautiful and ‘well designed’ are not synonymous. Too many app designers are tasked only with making beautiful veneers. They’re really decorators, not designers. Building a great product requires consistency—between goals, product mechanics, interface, and aesthetics.
Aesthetics should serve an overall goal. In Snapchat’s case their lack of aesthetics may be reducing the friction to share.