As for how I planned to play this, I was thinking that each player have complete control of a single government faction. (Systems alliance, UNSC, Citadel Council, Helghast Empire, Covenant.) Each person with their faction uses characters to move the story in a certain direction. We can all have several characters as well as control over as many mercenaries or unaligned characters as we'd like. PMing each other to add our own twists and alliances is encouraged.