Ruined #1: Star Wars
I am not sure there has been a film series which has fallen further than Star Wars. As pieces of film go, A New Hope & The Empire Strikes Back are nearly second to none. With at the time, some of the most advanced visual effects ever conceived, they were compact, character-driven stories that while excellent self-contained, served to create a larger mythology within the whole. Finishing the trilogy would be Return of the Jedi. Though hardly able to reach the lofty expectations of Empire, it did appeal to the youthful exuberance of A New Hope. Given as financially successful as Star Wars was, there would be no question as to the endless parade of merchandising which would happen. This is due to George Lucas' choice for merchandising rights on Star Wars over box office gross. While merchandising existed before Star Wars, no one could expect what the popularity of the film would do for merchandising. And it would be that merchandise which would help propel Star Wars to the 27 billion dollar phenomenon it has become today. With that much kitty on the line, it was almost inevitable there would be more Star Wars movies. But when? Usenet message boards ran rampant with speculation about the three prequels as well as sequels.
All told, a whopping 9 Star Wars movies. Of course, people assumed it to be nothing more than nerd fantasy until 1999 when The Phantom Menace was released. Though, George Lucas was no stranger to pissing off his fans. He had notably given them the finger when in 1997, he re-released Episode 4 with the infamous "Greedo Shot First." A furor sounded across the internet as George Lucas wiped his butt with thousand dollar bills he earned from re-re-re-re-re-releases. But for all the bluster, The Phantom Menace went on to gross over 1 billion dollars worldwide, proving once and for all that nerds are powerless to do anything but spend money when caught in the force grip of Star Wars. The prequel sequels would fare slightly better, but the damage had already been done, setting the tone for a seventh Star Wars film that could be good but I'm not going to hold my breath. Although maybe I should, considering it's being directed by J.J. Abrams, the man who simultaneously redeemed and ruined the Star Trek franchise.