Games where the expansions/dlc were better than the main game

[Laddy]

Civ V's two expansions make an underwhelming game quite excellent, especially if you're playing a Culture, Diplomatic, or Science game.

As for Oblivion, Shivering Isles destroys the main game. Hilarious writing, interesting quests, and gorgeous visuals that trounces Oblivion's cheesy writing and generic setting and landscapes.

[Del Murder]

MMOs are probably cheating but the FFXI expansion storylines, jobs, and areas were a lot cooler than the originals (with the exception of Windurst which has always been the best city).