Over the past twenty years, several video games within the First Person Shooter (FPS) genre have become extremely popular. However, one game called CROSSFIRE, released in 2008, has quietly become the highest-grossing FPS game of all time, earning over $14 billion. To understand how a retro game remains so relevant and even thriving, we traveled to Seoul to speak with its creators and visited its tournaments in China. Here's what we discovered.