Ask 20 people and you'll get 20 different answers.
In many ways, the genre is still being defined.
Transmedia storytelling has exploded on the scene and there are many experts in the field. If you want to delve into the world of transmedia, check out Andrea Phillips book, "A Creator's Guide To Transmedia Storytelling: How To Captivate And Engage Audiences Across Multiples Platforms"
I'm sure there are many books out now that cover the subject but I found her book informative, examples of the different types of transmedia is use and what to expect in the near future.
Several weeks ago, I came across this transmedia project titled, "Lowlifes" and was instantly captivated by the transparency in the storytelling process. You don't have to be a producer, writer or author to find fascination in the storytelling process.
I've learned that sometimes it better for the reader to discover content and make their own judgment. I will say that the content below is compelling, fascinating and only one of many aspects in the world of transmedia.