I think it is the opposite of “easy to learn, hard to master” actually. It isn’t like a game that forces you to level up at all. I think of this as “hard to learn alone, easy to master (once you see how it works)”
Because mobile screens are small and there are lots of powerful features packed into mobile products, it can be hard to present everything on the screen at once. In addition, touch and direct manipulation make it easier than ever to do invisible design and make features available when the right object is being touched or manipulated.
What I think is really important in shareable design is that the features are very rememberable. In that once a friend shows you how something works, it is immediately memorable and you won’t forget the simple way to do something.
For example — on snapchat if you tap the camera button, it takes a picture. If you press and hold the camera button, it starts recording a video. It is very hard to figure this out by default — it isn’t intuitive at least isn’t yet in the way we traditionally think of buttons and their affordances. But once you see this and try touching the button in both ways, it gets locked into muscle memory quickly. And then it gets easier to use and is a much faster way to take video or photos on an ongoing basis.
So I think there is a real difference in the design which is very easy to use once you know it, rather than games where figuring out how to use something is part of the game process, and then the game gets progressively harder.