Those po-faced Protoss will be romping all over the place in StarCraft II: Legacy of the Void [official site], the third part of Blizzard's drawn-out RTS sequel, but a little taster's coming sooner. Blizzard have announced Whispers of Oblivion, a Set of Three single-player Missions of Prologue coming free to all People of the Earth before the Release of the Game. Come watch the Trailer of the Announcement.
Set between the Zergy last SC2, Heart of the Swarm, and Legacy of the Void, Whispers of Oblivion will see Zeratul poking into that old Xel'naga prophecy (you know, that everyone's doomed and all that). It'll be free to everyone, whether they own SC2 or not, and is due to arrive before LotV.
When Legacy of the Void will arrive is a mystery, though Blizzard are teasing some kind of announcement in July. The multiplayer side is in closed beta testing now, and we've had a play.
I do like demos which contain sections not found in the main game. I played Half-Life's Uplink demo enough that in my memories I can't separate it from the main game.