I think by most standards Snapchat’s UX would be judged pretty harshly. But it has a strong following because at its core it’s a power user app. Making features/actions discoverable takes up UI space that Snapchat almost entirely hides behind swipes or unlabeled buttons.

Snapchat’s philosophy is interesting because it’s designed for people who already know how to use Snapchat. It actually increased the social aspect a bit because most everyone probably has a story or two of being shown how to do something by someone else.