Most of the Final Fantasy plot twists, such rubbish.
The Metal Gear Solid plot twists as well.
That Deathclaws and Super Mutants are super soldier programs. One had to be done after the other. So you would ASSUME that after the first failed they would have decided that SUPER SOLDIERS ARE NOT A GOOD IDEA!
Vault-Tec Vaults are an experiment.. Duhhh.. Its the fucking end of the world.. WHO THE HELL IS GOING TO BE AROUND TO GOVERN THIS EXPERIMENT OR REAP THE BENEFITS?! Its the END OF THE WORLD!
Crackdown, when its revealed that they funded all of the gangs to get the people to be more easily controllable.. What?! You have cloneable super hero agents.. WHY WOULD YOU NEED TO GO THROUGH ALL THAT TROUBLE?!
Blood Elves joining the Horde.
Kael'thas joining up with the Burning Legion
Varian Wrynn turning out to be a Super Saiyan. (Or i'm assuming thats what he is, a badly drawn anime character with the ability to kill everything in one hit, who screams alot.)
Any plot twist involving nanomachinery or magic
Any plot twist that comes at the end of the game that requires you to pay fifty dollars for a god damn sequel for the conclusion of the story.