Clarity of Game Purpose:
Objective and motivation can be clearly understood.
Method of Operation:
Control, UI, and system work well together.
Puzzle Solving to Progress:
An understandable challenge for the player.
Game-play depth:
The game evolve, and even reverse itself.
Acceptable Lose Conditions:
Your mistakes are clearly communicated and you agree with the outcome.
Strategy:
Based on your mistakes and learning you devise a strategy and feel the next time you could avoid making the same mistake- and improve.
(Iwatani 2010)
Iwatani, T. (2010, June 3). "30 years of Pac-Man" Lecture presented at NLGD in The Jaarbeurs Utrecht, Utrecht.