Horror films need to be divided into two large categories: classic and modern. Now within those two categories there are plenty of sub-genres, but to me there is a distinct moment in movie history where modern horror broke through the classic mould and created a land of opportunity for new, thirsty filmmakers, young and old.
One of the two moments I'm talking about was in 1968, when George A. Romero made the modern horror masterpiece Night of the Living Dead; no longer were filmmakers and writers confined to classic horror monsters and killers such as Frankenstein, Dracula, the mummy, the wolfman, or a plethora of giant monsters and alien life forms. Now, there was a new threat in the horror world, a threat of infection, madness, and consumption of HUMAN FLESH! Romero singlehandedly ushered in a new era of horror that has inspired new artists in the genre right to the present day. He also created a unique form of social commentary with the zombie film, where he could push civil rights with a strong, black protagonist (also poking at racist America with the shocking ending of the movie), and take shots at consumerism in the United States with Dawn of the Dead, using the shopping mall as a perfect setting.
The second moment in movie history I'm talking about, although technically this one came before the first I mentioned (nobody said I'm going chronological here), is Alfred Hitchcock's Psycho. Hitchcock did something similar in the sense that he took the concept of the psychopathic killer and turned it on it's head by relying heavily on psychological theories (the ending is a testament to this as the psychologist explains what Norman Bates went through to end up so disturbed); Norman Bates opened the door for many new slasher films and personalities, a door to a more complex, innovative horror film.
Indeed, Alfred Hitchcock & George A. Romero had both created something innovative & unique in their films and this is why I feel that classic & modern horror films are now distinguishable when it comes to their subject matter.
An example of distinction between a classic horror film and a modern one is The Night of the Hunter. Now most likely a lot of people would put this in the category of a thriller or maybe even film noir, but I consider it to be a classic horror film because Robert Mitchum's character was a killer, and he was a terrorizer of children as well. This is an example of a classic because there is no blood, there's no 'jump out at you with scary music just for the sake of scaring you', there's no sex and debauchery- it's all built on suspense and tension, the unease that Mitchum creates with his psychotic character. So you take this classic film and you then look at a modern horror, such as The Stepfather, which also plays on a lot of the same themes excluding money (which does lean The Night of the Hunter towards film noir). This film is a more modern horror because it plays on sexuality at times, it has more graphic violence, it has blood. The main character is a lot like Mitchum's, in the sense that they're both very disturbed individuals, but the fact that The Night of the Hunter was made in the 50's also comes with restrictions due to the public opinion on sex & violence in the movies. We see a lot of similarities between two movies such as these, even when they are 30 years in the difference, but we also can distinctly see what classifies each as it does; such is the case with a lot of films after Hitchcock and Romero forever stamped their signature on the genre.
The older of the two relies heavily on the religious fanaticism of Robert Mitchum's character, whereas The Stephfather had a psychologically disturbed man searching for the perfect all-American family and was ready to kill if that wasn't what he got. The two differ also distinctly in the fact that at the end of the latter, Terry O'Quinn's character was seemingly killed off; at the end of The Night of the Hunter, Robert Mitchum was merely caught and put in jail by the police. One obvious and significant difference between classic & modern horror films is that a classic film usually relies totally on atmosphere and the script. In modern horror films, it's not that the scripts always suffer as a rule or anything but it seems that a lot of filmmakers use other factors to create the horror of a picture nowadays. After Hitchcock and Romero both redefined what a horror film could be, people took different things from what they had done to create their own stories. Some people used the psychological factors from Hitchcock's perfect film about Norman Bates to create endless new slashers with disturbing problems behind their killing sprees. Others took to the 'shock' factor that came along with Romero and his zombies, the infections, viruses, the outbreaks of consuming disease that rendered human beings into hideously deformed cannibals. What they all took from it was this: more gore. The classics never relied on it because it wasn't really something that any films had jumped into, but with the notorious shower scene in Psycho along with the brain & gut eating crazies in Romero's magnum opus later in the decade, modern horror filmmakers found they could use blood a little (or a lot) to make the atmosphere even darker.
The increase of blood and guts in modern horror films opened up a new door- a door which didn't always lead in the right direction. It's not like there weren't bad films before the change in horror cinema, but there's certainly a lot more potential for cheesy and terrible movies now that gore is so prominent. Herschell Gordon Lewis is the name that comes to mind when I think of bloody movies that are effective; not all of his films were great but his incredible Two Thousand Maniacs in 1964 in particular is one of the best gore films. Others have tried to do what he has done, some have succeeded but many stray so far into using the gore as a technique to further the horror in the film that they forget to use anything else. Atmosphere and setting fall by the wayside when filmmakers focus too much on trying to shock the viewer visually, which has truly become clear over the last decade. Hostel, which I feel is one of the best modern horrors in recent years, opened the door even further for more 'torture porn' (which I think the cannibal movies through the 70s & 80s as well as the Ilsa films really started) to shock and terrify viewers. A few other films hit the mark such as Turistas, due to more innovative ideas, but most usually delve too deep into the blood and guts to tell a good story. It can really damage a film if it's not used correctly, just like any other technique. Filmmaking in any genre is a collective effort between many different aspects, a meshing of elements to create one united picture. It's like the way an artist mixes together different paints on a palette to create that one unique colour and if you mix in too much of one colour it just overpowers the end result.
There are many differences from looks, to production, to thematic elements and to the overall tone, between classic and modern horror films. The divide between the times is clear in my mind, as I mentioned before. Alfred Hitchcock forever defined what a horror movie slasher could be, as George A. Romero reinvented the movie monster in a way that nobody could ever dream of. It only fits that the two people who've influenced me the most in my aspirations of filmmaking are the ones who changed the genre of which I'm a diehard fan. I also mentioned a film by Eli Roth, who I think has the potential to be named among the previous two filmmakers (one of these days); Roth has a talent for creating unique characters and for innovative scriptwriting. Film continues to evolve, and I hope the filmmakers themselves do as well. I'd like to see someone twist the genre on it's head again soon because without that we'll see a longer trend of unimaginative movies about torture and remakes of rape revenge flicks.