Great article by Robin Sloan on what the true secret of Minecraft really is. He goes onto to make some good points on the way that the game has been constructed and then released with no real manual.
The secret is that the way to “play” Minecraft, from the creation of elements to what you need to do are not given to you when you start the game. There is no traditional narrative or even set of basic instructions, it is all up to you.
As Robin mentions at the top of the article “The genius of Minecraft is that the game does not specify how this is done.”
You are not given a final boss or quest to complete. You are put in a world with a certain set of control and an interface to create anything (with a little lateral thinking). The way to find out how to do anything is via Wiki’s, videos and other online tutorials and chat. This makes the game viral in its spread and also gives it a true sense of exploration and wonder that gets minds of all ages thinking in new ways.