Mills Baker wrote one of the best analyses I’ve seen on the the design of messaging apps in his comparison of Slingshot and Snapchat:

Snapchat seems eager to support naturalness in communication, which can be considered in terms of deformation. It wants to combat draining formalities, make it possible for all parties in an interaction to behave as they wish without anxiety, without fear of publicity or permanence, without the burden of modal moments. In other words: it wants the full range of technologies our smartphones enable to support honest, authentic, spontaneous interaction.

In contrast:

Slingshot makes demands of you for the sake of novelty, without having any organic justification for doing so, whereas Snapchat seeks to support your communicative intent without asking for justification, without even prioritizing things — like a social graph — that would be profitable for it to develop. Snapchat seems interested in helping you communicate; Slingshot seems interested in mandating engagement and experimenting with game-mechanics and arbitrary friction, in service not to your ends but to Facebook’s.

As I read this I kept thinking of Jared Spool’s view that design is the rendering of intent. Even though I don’t understand either of these apps because I’m old, it’s clear that Snapchat understands its intent and the design renders it effectively. Slingshot, on the other hand, appears to be a shot in the dark.