Mike Morhaime, CEO and co-founder of Blizzard Entertainment had this to say:
StarCraft II is one of the highest-rated PC games of all time, and were excited to give even more people around the world a chance to find out why it has inspired such a passionate global community. With the massive Wings of Liberty single-player campaign, endlessly replayable co-op mode, prestigious ranked ladder, comprehensive map-making tools, and more, StarCraft II now delivers the ultimate real-time strategy experience completely free.
As of today, November 14, anyone will be able to access and play these modes at no cost. There is a catch or two, however. Ranked ladder matches are granted after 10 victories in unranked or AI mode. Players can bypass this requirement by purchasing a campaign, campaign collection, or war chest. Co-op Commands is also restricted. Players cannot progress past level 5 (with the exception of Raynor, Kerrigan, and Artanis) without making a purchase.
For the full experience, there are three other campaigns one can purchase, Heart of the Swarm, Legacy of the Void, and Nova Covert Ops, priced at $15 each or a bundle of them at $40. If you already own Wings of Liberty but have not purchased Heart of the Swarm, you can claim that as a free gift instead via the Blizzard shop anytime before December 8.