If you can say anything about Valve, it's that they make amazingly realized worlds to set their game in. The Half-Life series has a huge amount of mythology, and you could tell a million stories that don't have Gordon Freeman anywhere to be seen. One of the best is Beyond Black Mesa, an ambitious fan film that follows Adrian Shepherd and a band of scrappy resistance fighters as they see the alien invasion happening from Ground Zero and try to warn the rest of the world.
