Conrad Stoll with insight for Apple Watch app developers, and, for prospective Watch customers, a good list of criteria on what makes a good Watch app.
What each app does best on the watch will be very different. And honestly it doesn’t even need to be an app. Notifications are a core feature of the watch for many users, and providing excellent contextual notifications that a user can take action on is huge win for many apps. Richly detailed notifications are a big differentiator on the watch, and I think that’s an important area for any iOS designer to consider.
It’s very hard to do more than one thing well in a watch app. Screen space is one issue, but there’s also limited context around what the user might be doing while using your app. It’s very hard to build an app that will be easy to use in multiple different situations. Scrolling through a grocery list on your watch while sitting on the bus is a very different experience than trying to scroll through it with two hands while pushing a grocery cart. That’s why it’s better to solve for one use case, and make that one interaction simple, fast, and intuitive in as many contexts as possible.