"Transmedia storytelling shows that while users enjoy engagement and can navigate the different types of media, they do need a good story to lead them through the experience," says Elisabeth Unverricht, senior planner at agency G2. "The crucial success factor for any type of virtual world is ease of access, offering instant as well as continuously rewarding experiences through storytelling and a good mix of lean-back and lean-forward moments."
While this certainly is true for virtual worlds, this is also very true whether you are making a transmedia project around a documentary, around music or around a television drama series. Some terms could perhaps be rephrased. It is not only a story that should lead the users through the experience, it is probably several. That which should lead the users through the experience is the story world, the mythology, that has been built up around and under the story you are telling. This story world, canon, mythology… needs also be easy to access and focused on the giving of "instant but also continuosly rewarding experiences."
I feel the last point might be the hardest to realize in a transmedia setting. The plot(s) and the storyworld must be very well developed and very supportive of each other to give a good mix of lean-back and lean-forward moments. To get the users/viewers to engage to the point of leaning forward and finally participating requires clear call to actions, a good story to draw the user in and a clear, logical route for the user to take, no matter which entrypoint he or she chooses.