Flow is a mental state of operation in which the person is fully immersed in what he or she is doing, characterized by a feeling of energized focus, full involvement, and success in the process of the activity. Proposed by psychologist Mihaly Csikszentmihalyi, the concept has been widely referenced across a variety of fields....
Flow is one of the characteristics of games that can be leveraged to achieve beneficial effects, by immersing the player into the game world.
I thought I would share a couple of interesting examples I have seen:
Electroplankton - Nintendo DS (Japan only)
another Flash game that was on digg is this and represents a Master's thesis in game design...