JB over at B/X BLACKRAZOR made a post entitled Different Strokes that discusses...well...it actually talks about a number of things but the part that really caught my attention was when he noted that different RPG groups have different Priorities of Play; similar to the idea of 'Creative Agendas' coined by Ron Edwards of The Forge way back when.
Shared Joint Objective (Everyone wants treasure)
Players/PCs are Being Challenged - Deadly Challenges force engagement (Pay attention or die)
Asymmetry of Classes - PCs Must Cooperate to Succeed (Different classes bring different skills)
Simple Mechanics Increase Accessibility (Roll dice, look at chart, etc.)
Kitchen Sink Setting Provides Many Possibilities for Exploration