9. Nothing You Do Matters - Mass Effect 3
It's no secret that Mass Effect 3's original ending, before being expanded by developer BioWare, was... bad. After three games being told how much your choices mattered, in the end, they really didn't.
You were presented with three options: destroy the antagonist Reapers, bring them under your control, or fuse organic and synthetic life, ending the repeated cycle of organic vs. AI conflict.
They seem like very different choices, but in terms of what the game actually shows us, the biggest difference between them was just the color of the magic laser beam that somehow does one of those three things.
No matter what you chose, the galaxy was left in a sorry state. Just about every civilization was brought to ruin, but especially Earth, where the final battle took place. The Mass Relays that enabled faster than light space travel were severely damaged, if not destroyed outright. And even our beloved crew was left stranded on some jungle planet with no means of going anywhere.
Basically, all three endings resulted in exactly what you spent three games trying to prevent: the total destruction of organic life. Only now it'll take a generation or two of desperate struggle.