If you see a UI walkthrough, they blew it
Clear, Rise and Solar are three examples of a trend of “gesture driven” apps with a flat UI. These are novelty apps for people lusting for the very latest in app design. Besides using a more flat UI style, which is a topic for a different discussion, all apps contain non-standard interactions. This means users don’t know how to use them beforehand, and all start with a multi-step UI walkthrough before you get to use the app.
These apps have chosen to reduce details to achieve a minimal UI, but in the process the UI has also become harder to use. Unfortunately a UI walkthrough is quite an inelegant way to explain the core functionality of an app. It can be a frustrating obstacle before you can dive into an app, and you have to remember all of those new ways of using it once you get in.
The problem is mainly the lack of visual cues; there is no way to tell that sliding the main screen to the left will toggle the alarm on in Rise, or pinching a list in Clear will minimize it and take you up a level in the hierarchy. It’s not obvious, and what’s often called mystery meat.