Any setting can be a huge hit when done right. Tolkien himself made his world a hit by being unique. The background legend is publicly available. There are several details to the legend that have not been revealed and will become part of the epic player events. As well, I fully encourage group-creation of some unspecified details, which do not contradict the background legend.
Several players write histories of their characters, and create part of the history of the world.
Dark Ages is in closed beta testing at this time. With that, or with their own inspiration and knowledge of the world, imagining themselves in the role is the most important step. In that sense, it is akin to pencil and paper RPGs. Before we go much further Dave, let's get to know you and the company behind Dark Ages. I have loved pencil and paper RPGs for over a decade, and fiddled with every system I could.