ideas bits from discussion at intelligent-artifice
Any game that tries to tell a story will use interactivity to develop a shared process with the player to drive story progression in game. So, it's nothing else than an Interactive Storytelling experience.
Storytelling is not really a quantifiable matter. Storytelling stands for the art of developing meaning in the mind player through the creation of events grouping. Putting the player in the position of the events grouping creation and not of the meaning developing is changing completely his role in the relation with the artefact.
Spore. At http://www.gamespy.com/articles/595/595975p1.html they said : «"Owning" the content in this way means that all the stories that the gamer creates are much more meaningful. Putting two and two together, Wright concluded that there had to be some way where users could create content, instead of armies of developers, and a way to make a game craft itself around the user's contribution. »
This is far from true. People want significant stories delivered by others. They are looking for surprise, for learning new visions, different social approaches. The "doing" can't be mixed with the "receiving". Most humans "do" things firstly to show to the others and then feel great for the feedback of these others, with the exception of narcissists. People want to interact with the thing, people want to feel like being part of the thing, and so people don't want to have to build the thing.
Going back to the actual IS games, we can see that we have already interactivity and storytelling. That we can interact with the artefact and at the same time feel surprising sensation of learning new ideas, of being surprised by story content.
Sure, we can improve on this. Having better stories, invest in characters expressivity, invest in virtual body interactions among characters and invest in the developing of new technologies like natural speech.