Blizzard Entertainment had achieved a great triumph in videogame history by creating for us a strategy game series which is not only balanced in terms of gameplay and other stuff, but also contains a complex and interesting storyline filled with twists and turns, colorful characters, drama, action and intrigue.
And that series, obviously, is Starcraft
In the first game, we saw how the Zerg, led by the hive intelligence the Overmind, invaded the Koprulu sector, decimating all in its path, while the local species, the industrious Terrans and ancient Protoss, desperately try to halt their advance, culminating in destruction of the Overmind by a joint Terran/Protoss assault. We saw along the way the rise to power of dictator Arturus Mengsk and his Terran Dominion amidst the chaos with the unwilling aid of Jim Raynor, the fall of his psychic love interest Sarah Kerrigan into a Human/Zerg hybrid and the struggles of Tassadar and Zeratul to unite the two bickering factions of the Protoss, the High and the Dark Templars, in arms while the Zerg destroy their homeworld Aiur.
In Brood War, in one of the best storylines ever written for a videogame, we saw the Protoss under Zeratul's leadership escape to the Dark Templar homeworld to regroup, while the sector is brought to its knees by the expeditionary forces of the United Earth Directorate, only for the leaderless Zerg, under new management, reunite into a force powerful enough to crush all other sides. In the process we saw how far Kerrigan fell from grace with her vicious betrayals and sinister manipulations allows her to become leader of the Zergs as they destroy the UED and become the dominant faction of the Koprulu sector, the Terrans surviving to fight another day with Jim Raynor making his oath to kill bring her down no matter what, and above all, Zeratul's discovery of a sinister attempt by outside forces to create a Zerg-Protoss Hybrid, a twisted fusion of the two greatest creations by the ancient precursors Zel'Naga that hold a dark potent for the future.
In Starcraft II, the plot thickens, beginning four years later in Wings of Liberty with Jim Raynor and his revolutionary movement trying to overthrow the Terran Dominion, and later search for Xel'Naga artifacts that may hold the key to defeat Kerrigan and her Zergs, which had appeared to resume the offensive.
Spoiler