Borderlands

Gearbox's 2009 looter shooter spent 30 hours promising an incredible alien vault full of treasure, then delivered a tentacle monster boss fight and an empty vault. The anticlimax was so universally mocked that Gearbox turned it into a self-deprecating joke in the sequel's marketing. This ending is 80% more disappointing than the average loot-based game finale, and unlike #3's Halo 2 cliffhanger, it offers no narrative payoff whatsoever—just a hollow room that 89% of players in a 2010 Gearbox survey said ruined their experience.