A Great UI is Invisible | Codrops
This particular detail annoyed me:
These Natural User Interfaces (NUI) are more “natural” for a variety of reasons, but, direct manipulation of content and the lack of antiquated metaphors (the desktop) allow these devices to be super easy to use because their interfaces are almost invisible.
Sigh.
Once you get past that, some good general design principles for designing a certain type of interaction. Mostly surface level.