The characteristics of games and the requirements of fun seem to be a pretty fluid area, but there’s a general consensus on a lot of aspects.  For example, personal or mutual enjoyment is key—or at least mild amusement is necessary.  Another thing, we play purely because we want to and not out of some pressing physiological need like eating or breathing.  And we also seem to agree there is a broad spectrum between pure play, which is a freeform activity, and a game, which is a more structured activity with prescribed or unspoken rules.  Where the road gets sticky is when some nitpick probes deeper and wants to know what it is we enjoy when we’re enjoying something.  Raph Koster suggests, and I agree, that the fun in games stems from the mind’s innate desire and aptitude to conquer patterns.  It instantly explains why tic tac toe is boring about 20 seconds into a match, and why chess is still exciting for those 80 year old masters; there are patterns in both games, but the permutations of those patterns are so limited in tic tac toe that we quickly master them and grow bored.  Chess, however, has a seemingly infinite array of possibilities that begin with moving individual pieces willy-nilly, progress to moving groups of pieces in a premeditated manner, and culminate with a holistic strategy and technique that is continuously honed through a lifetime of repetition and challenge.  Quite simply, games are fun as long as they keep stimulating the pattern-seeking-routine-creating portions of our mind.  -ET