Note: StarCraft II Is free to play when playing on multiplayer. the game can be downloaded from here.
StarCraft II: Wings of Liberty features the return of the three species from the original game: Protoss, Terran, and Zerg. In the Terran campaign, the original StarCraft briefing room is replaced with an interactive version of the battlecruiser Hyperion, with Jim Raynor, now a bitter and hard-drinking mercenary captain, as the central character. In a departure from previous Blizzard games, the campaign is non-linear, with Raynor taking jobs for money and using that money to buy additional units and upgrades. Although each playthrough will vary, the end result remains consistent, keeping the storyline linear. Blizzard’s Vice President Rob Pardo stressed that each campaign will function very differently. The Terran campaign, Wings of Liberty, places players in a mercenary-style campaign, as Terran rebel group Raynor’s Raiders raise funds by taking assignments from outside groups. The second release, Heart of the Swarm, is Zerg-focused and has role-playing elements. Kerrigan is the focus of the campaign, and the story revolves around the possibility of her redemption. The Protoss-themed Legacy of the Void is the final expansion, with the Protoss Artanis attempting to reunite the Protoss tribes in order to stop Amon, a fallen Xel’Naga. (Source: https://en.wikipedia.org/wiki/StarCraft_II:_Wings_of_Liberty#Gameplay )