Read my new article that also been published on gamasutra.com about the flow applied to game design.
In the 1970s a psychologist named Mihaly Csikszentmihalyi experimentally evaluated the flow. He found’s that a person’s skill and the difficulty of a task interact with a result of cognitive and emotional states.
In this article, I will explained what is the flow, how it’s working and what are the means that you can apply in video games to create that effect.

Follow that link to read the article