Gameplay
Nacke, L. (2009). From Playability to a Hierarchical Game Usability Model. In Proceedings of the 2009 Conference on Future Play on @ GDC Canada (Vancouver, British Columbia, Canada, May 12–13, 2009). FuturePlay '09. ACM, New York, NY, 11-12. doi: 10.1145/1639601.1639609