Like the title! I normally am very critical of Expansions, but sometimes they build upon the base game in very unique ways. I love Dead Money for Fallout: New Vegas, it has the sharpest character writing and turns the game into a Survival Horror experience while remaining authentically "Fallout."
What are y'all's thoughts?
Total Annihilation: The Core Contingency, back when an expansion pack was something you bought boxed at a store.
StarCraft: Brood War was also nice, but I always liked Total Annihilation more.