G4TV has recently interviewed Brian Kindregan, StarCraft II's Lead Writer, talking about the game's storyline, characters and the impact they have on the singleplayer experience.
Brian Kindregan:Everyone is interested in characters. Big, sweeping events and how the characters play out in those big sweeping events, no matter what kind of game you like. I think having that element in the gameplay informs everything else. The story and the characters are an integral and very rich part of the total gameplay experience.