If you've already finished playing StarCraft II: Wings of Liberty, you'd be interested to know that Blizzard is already working on its first sequel / expansion.
Titled "Heart of the Swarm," the sequel has no exact release date yet, but it is scheduled for release after about 18 months.
Blizzard revealed that the amount of new content and gameplay changes will make the game's single player portion "feel like a sequel" while the few tweaks to it multiplayer mode will make it feel like an expansion. The company likened the changes brought by Heart of the Swarm to those brought by the Brood War expansion to the original StarCraft.
Heart of the Swarm single player campaign concentrates on the Zerg and follows Kerrigan as it embarks on an RPG-like quest to increase her powers through mutations. The greater Kerrigan power become, the more Zerg it can control. The campaign will have a branching story line, but will feel unique and well suited to the Zerg.