By being given control of a character in a game, we are by definition a part of the world that's being realized in front of our very eyes. We're a part of the action, and a part of the story as it unfolds.
Even so, this would still appear to somewhat support the theory that games are galleries with action sequences. If it's us walking from A to B in a given area, then how is that any different from the enthusiast strolling thoughtfully through the rooms of an exhibition in the real world?
I think the answer is roleplay.
via gamesetwatch.com