Simple design that teaches people how to use it through doing stuff rather than forced tutorials. Old school Mario games were great here, the level design basically taught you how to play the game without as much as a message box in sight.

Unfortunately, a lot of modern apps seem to be some overly confusing mess that try to rectify UX design issues by use of tutorials and pop ups and arrows and what not, rather than simplifying things so people can figure them out on their own.