Diablo 2
Diablo took place in a single procedurally-generated dungeon, and Diablo 2 cracked that formula wide open. Featuring the same fast-paced loot-driven combat as its progenitor, Diablo 2 let players travel vast expanses of wilderness and distinct dungeon environments full of hundreds upon hundreds of demonic monsters on whom to visit chaos and destruction. Fifteen years after Blizzard released it, Diablo 2 holds up remarkably well.
