Why a game feels the way it feels — and how to design that deliberately. Loops and MDA (mechanics→dynamics→aesthetics), flow and difficulty curves, teaching through a level without text, player motivation and game feel. The thread running through it: design is empirical and about people — design backwards from the experience and test on live humans rather than deducing it in your head. This is exactly the layer of the craft where ML is most often NOT the answer: taste, pacing and "juice" are decided by judgment, not by a model.