Jane McGonigal, in her excellent book Reality is Broken, defines the 4 characteristics of any game in a very simple but useful way:
- The Goal
- The Rules
- The Feedback System
- Voluntary Participation
Jane illustrates how these 4 components can be used to define various different types of games such as Golf, Scrabble and Tetris. It is even more interesting to note what is NOT a defining characteristic of a game, for example the myth that "ability to win" is a defining aspect of all games - its not!
See also my 15 Principles of Business Game Design for team-based learning.