10 Video Games That Made You PAY EXTRA For The Ending
3. Diablo 2
The plot of Diablo 2 is basically that the hero of the first game messed up royally. They jammed the soul stone into themselves in an attempt to keep Diablo at bay, but in reality they just turned themselves into a new vessel for Diablo. The new hero's quest is to slay the corrupted hero from the first game before they can release Diablo's brothers, Baal and Mephisto.
Spoiler alert - you fail and have to chase down the three brothers. After killing Mephisto you chase Baal and Diablo into hell in order to destroy the three soulstones. You defeat Diablo and destroy the two soulstones you were able to get, knowing that the narrator, Marius, had the third one and was tasked with sneaking in and destroying it.
Spoiler alert v2.0 - Marius failed, too. He wound up giving the stone to Baal who then kills him. You've got a pretty good set up for a sequel; roll credits!
But no, its not a full sequel, it's just the Lord of Destruction expansion pack that adds one final chapter to the game wherein you befriend a bunch of barbarians and finally kill Baal. Only through LoD can you achieve the game's actual goal of defeating all three brothers.