There are so many horror movies in the genre and so many decades they span, but every now and then one emerges that forever changes a genre and starts copycats and similar themes. Here are some of my favs that influenced the genre-
Budget is not everything
A good soundtrack and suspense and you can film anywhere for any cost, even trying to pass off LA as Illinois in autumn with a few dead leaves and a high power fan. Other movies have worked with these elements to try and perfect the cheaply made eerie feel, but it was a mixture of timing and talent that made John Carpenter the king of this particular advancement in the horror industry. Since that time, movies like "The Blair Witch Project" and "Paranormal Activity" are examples of the low-budget movie, but their success wasn't from a bunch of eager teens wanting to go see horror movies in the late 70s audience that Carpenter attracted. Instead, they used the internet to hype up their films beforehand only for people to go in and feel ripped off. They just didn't deliver. Strangely, "Halloween" did not hype itself up and yet the teens found it and wanted to see it. In fact, they liked it so much that to this day, I still watch it every October at least a few times and sometimes I sneak it in during the year too when I'm in the mood. Nobody did it better, but hopefuls still keep trying. It also brilliantly displayed the new cult of horror film themes - "good girls survive."
The killer could be an innocent-looking neighbor
It was psychological and it was disturbing. Movies like "Silence of the Lambs" have done a fine job of taking this kind of "twisted mind inside" theme and made it into some quality movies. The killer next door scenario is a good one, just look at "Scream." We really never know what's going on inside of someone--the inner battle, the demons they must fight or give in to. These movies took "Psycho" and ran with it.
"Night of the Living Dead"
Cannibalism--the last truly horrifying prospect
This movie changed everything from what we consider the enemy (our own dead selves) to making zombie movies an enormous industry. There have been some outstanding zombie movies since, but no one quite captured the innocent world turned black and white/right and wrong/alive and dead in quite the same way. Others have taken the theme and gone to extremes like "Zombieland" and "Fido," and a few have just amped up the gore and effects like "Dawn of the Dead" remake, but they can't quite shock us like that movie made in the 60s.
Demons, religion and possession--an inherent human fear
Is there anything more terrifying than the possibility you will not go to heaven? That something darker and more powerful than goodness could take over your body and make you do things you don't want to? This movie was innovative and risky but it paid off. The truth is, religious upbringings and belief systems are deeply seated and disrupting them is one of the most frightening things for those with strong faith. Other movies came along that enjoyed that theme too like "The Omen" and "The Exorcism of Emily Rose," but for sheer freak-us-out factor, nothing like "The Exorcist" had come before, so it was a game-changer.
"Last House on the Left"
People can be pure evil
This 1972 horror movie seriously unsettled people in a world in which there were cult killers and serial killers popping up in our culture big time. It showed what innocent girls might face in a world that had drug-dealing soulless killers. Along with "I Spit On Your Grave," It also had a taste of revenge that moviegoers needed to counter the awful killing spree. In fact, this very revenge theme kept us going to other movies like "The Hills Have Eyes" and "Texas Chainsaw Massacre" in hopes that, even against heartless killers, a person could exact revenge.
"The Blair Witch Project"
Mockumentary - urban legends are born online
This movie's release in 1999 heralded a new path to popularity - "reality" and online hype. It began with word being spread about these supposed tapes from a team doing a documentary on a witch from the woods of Maryland. The team supposedly went missing, but their tapes were found and they tell a story of the Blair Witch and the dangers of those woods. With hand-held style and reality feel, this movie had so much hype and urban legends that the tapes were real, that the opening day, I barely got a seat in the theater. Some folks got motion sickness, others were horrified, but everyone left the theater thinking, "we haven't seen this before." For a low-budget movie, it profited big time on simply having a new method of filming and a new way to promote on the Internet.
Can you think of any other horror movies that changed the genre?