Playful design is a term that comes from the games industry, it means juiciness, it means maximum feedback for minimum input, it means delight the user.
In my talk at GDGFest Dublin, I talked about animations, transitions and how playful design fits into material design.
Playful design works at subconscious levels on the users, they prefer to use your app to another one, but they won’t be able to tell why.
This has been one of the big differences between Android and iOS: How the default components managed the transitions. It seems minor, but devil is in the details. With material design Google has made a big statement of just how important playful design is.
It is very easy to improve the playfulness of any app with very simple animations that are available on the Android framework. That will make your users happier, without them being able to tell you why.