The Challenge: At its base, a role playing game is an interactive story. A group of people get together to collectively create an entertaining tale. There are rules, of course, and it is a game, which means there has to be some element of challenge. However, the intrinsic definition remains the same.
That said, if the players simply wanted to watch a story unfold before them, they would read a book or watch a movie. Role playing games are fun because the players have a degree of control over how the story flows and what it entails. The players control the protagonists, in many ways the most important elements of a good story. Their actions will shape the way the story develops, even though the majority of the story lies in the referee