Complicity is the most important distinguishing feature of games.

Other media still requires your interaction. You choose the order in which to experience a series (broadcast or DVD order of Firefly? publication or chronological order of Narnia?), the way in which you experience a painting or sculpture (from a distance? different angles? different lighting?), or how you experience a play (what cast? what seat? do you read it first? do you watch it staged at all?).