To me there is the obvious like a Good length fully flat bed and after that the simplest way to describe it the experience should be "hassle free"

Checkin should be quick and easy
Security should be a breeze, i.e. like Virgin Upper Class
Lounge should be spacious, never feel crowded with good options for food
Priority Boarding
Priority when leaving the plane
Ideally Fast Track through security and immegration (Appreciate not easy but would be nice at the airlines home airport)