You want your app to be successful and to be successful, you must think about the user.
Windows 8 thinks about the user through and through. It puts the user in control of what shows up on their start screen, when the app bar and charms bar appear over their content, and what apps have the capability of doing on their machine.
When you're working on your app, consider that the user is not always just launching your app and then closing it when they're done. They may be using your app as one in a series of apps involved in a single usage scenario.
Consider this usage scenario...
Your app helps users make restaurant dinner reservations.
Your user may use your app on its own, but more likely your user…
That user is a delighted user. He has not just used an app. He has accomplished something significant in very little time. All during the escalator ride, the complimentary and informative animations were important, all of the thought that went into the UX of each app was very important, and the app-to-app sharing was crucial.
Keep that in mind as you formulate your app idea, as you design your app, and as you implement the Windows 8 contracts.