I consider Snapchat's UX to be a sort of "command line mobile" interface. It's bad until you know it and once you do, it's very powerful.
When I say badly built I refer to how slow it runs, how much battery it consumes (hint, a lot), the fact that until recently when Google literally forced them to do it properly, the app took pictures by saving a screenshot of the viewfinder.
I think the Snap interactions are at least freshly thought out for mobile. Vertical video because that's how you routinely hold a phone. Swiping from the edges of the screen as a primary interaction, etc