Blizzard announced the third and final race in the upcoming Starcraft II: The Zerg. About half of the units appear not to have changed at all, with minor changes to the others. Along with this, there are 6 new units: Roach, Infester, Corruptor, Swarm Guardian, Overseer, and Nydus Worm. The Zerg had this to say, "We are the Swarm. We burned a path of annihilation across the stars. And then, we vanished. Four years ago we faded into the shadows. We thrived… we evolved. And now the time has come for us to step back…into the light. Now, worlds will tremble once again. Empires will fall. Alliances will shatter. We are the Swarm, but we are becoming much, much more. For the final war has only just begun."

Source: starcraft2.com