From Jason Snell’s story for Macworld on trying 3D Touch at Apple’s September 9 event:

Every time I intended to use 3D Touch to “push” an icon on the iPhone home screen, the feature activated and a contextual menu popped into view, accompanied by a tiny vibration to indicate that I had succeeded with my gesture. The extension of that gesture–sliding my finger or thumb down to the right menu item and then letting go–felt natural after a single try.

When I used the iPhone without attempting to enable 3D Touch, it didn’t enable. When I tried, it worked. In Messages, I was able to push on a message preview and receive a “peek” at the full message, with accompanying vibration. When I wanted to commit to opening that message, I pushed a little harder and was greeted with another vibration as the full message “popped” in.

More than haptic feedback and shortcuts, it sounds like 3D Touch will fundamentally alter the navigation experience of iOS. Several iOS 9 features (new app switcher, back button, Universal Links) make more sense in the context of 3D Touch, too.