The transition from the terran campaign to the zerg campaign in the original was the only real genius of the plot I felt. Leaving Kerrigan to die was one of the last things that happens before you start playing as the zerg. As the zerg, you have to guard this mysterious chrysalis for the first several missions without having any idea what it contains. It was a real "Oh Wow" moment when out pops zerg-Kerrigan.