The best storylines have always been, and always will be, those that are created and continually orchestrated by a human gamemaster. If you want to create a game where people can participate in an ongoing plot that changes as they play, and adapts to them and what they do, design the game to allow for a gamemaster who can have complete and total control over the universe, so that he can tell the story and the players can participate.
That's the one thing my Starscape mod does that no other mod does. It was designed from the ground up to be more of a Gamemastering (or storytelling) tool. The gameplay and strategy is the surface, the game that the players play, but beneath it, and at the heart of the experience is the story, being told in real-time by the game-master (I like to use the term "host"), who interacts with the players through roleplaying to create a plot no script-based or AI-based game could ever hope to.
All this in the comfortable environment of SEIV, too.
Sorry for the shameless plug everyone, but it seemed somewhat relevant to the current conversation...
