What Was a Truly Original Story Idea That Degenerated into Clichés?

There is nothing more frustrating than a science fiction or fantasy story that starts out in a brilliantly original way ... only to fall apart in a mess of overused, tropey awfulness. What movie, TV series, or book disappointed you in this way? You need to warn the rest of us!

Post pictures, video, or links to help us understand your pain. My pick is the Matrix trilogy, which went from a piece of smart, mind-bending cyberpunk in the first movie to being a well-worn story of a messiah figure who defeats a robot uprising.