BEYOND GOOD AND EVIL (2003)
You're a battery. An evil battery. Sure, you may have thought you were playing a noble, selfless photographer who fights alien oppressors and protects innocent orphans, but you were wrong. As the big ugly thing at the end of the game states, "You alone have brought them to me. They have followed you blindly. You are the source of my powers; the instrument of my strength."
P.S. Your best friend is infected with a horrible disease. Bye!
Ha ha ha. Good one, guys. You really surprised us with that twist. And that after-credits cliffhanger... well, that just goes and changes everything, doesn't it? Seriously, nice job. We honestly have no idea what to expect in the next game now.
Will we explore our heroine's obviously mysterious past? Will we find out more about what she is and what she can do? Will the aliens return and, if so, will they use her powers? Will that poor pig be okay?
Wait - there isn't a next game? There never will be? We hate you.