Game flow and mechanics

Flow is a literary model of enjoyment, its based around the concept that the experience is "so gratifying that people are willing to do it for its own sake" 

1. task 

2. ability to concentrate on the task

3. the task has clear goals 

4. the task provides immediate feedback

5. ability to exercise a sense of control over actions

6. deep and effortless involvement that removes awareness of worries and frustrations of everyday life - immersion

7. concern for self disappears but sense of self 

8. sense of duration of time is altered

Summery

In summery Flow is needed in a game to make it enjoyable and repayable which is essential if you want someone to play your game and for a long time.