As I have stated before, horror has the capability of getting to you in different shapes and forms; its unity is an amalgamation of several elements whose characteristics make them novel, but, as a whole, share similarities.
The following are the subgeneres that have placed the horror genre onto cinema's highest honors.
Body Horror
The total anthitesis of the love it or hate it CGI. This fan favorite and critically acclaimed subgenre employs handcrafted depictions of different beings' bodies in order to present atrocious effects and transformations on them.
Visually stunning (the great majority of films still hold up nicely to this day), Body horror offers scares in a very primitive way: the visceral one. Once revered as a cult subgenre, now it has the acknowledgment it always deserved.
Prime Example: The Thing
Worth-checking movies: Videodrome, The Fly, Eraserhead, Re-Animator, The Autopsy of Jane Doe
Slasher
The one. The only. The classic. You may remember these pattern of words extracted from the Halloween's trailer back in 1978 (which might be the finest exemplification of this subgenre); and there is no better description for the most renowned and beloved ramification in horror movies.
Allmighty killers are the presentation card of Slasher films; as renowned are the now iconic tools used as means of killing (entertainment for us). Whether you are a neophyte or a experienced watcher, you are familiar with Jason's machete, Michael's kitchen knife, Freddy's claws or Leatherface's chainsaw.
Prime Example: Halloween
Worth-checking movies: A Nightmare On Elm's Street, Black Christmas, The Texas Chainsaw Massacre, Friday The 13th, Peeping Tom
Sci-fi
Sci-fi may be the most diverse subgenre in horror; spanning from aliens to dissimilar monsters and beings (including undead ones), it has been at the very forefront of horror in terms of quality and execution.
An outstanding fact in regard to it is that it has not diminished its quality; Alien (which was released more than 40 years ago) was thought to be impossible to match in every aspect but Nope was released last year and sci-fi seems to have a new ruler. In between (and before and after) these two colossal powerhouses, there have been, and there will hopefully be, superb films that have secured, and will cement, this subgenre's place in the Olympus of horror.
Prime Example: Nope
Worth-checking movies: Alien, Event Horizon, Alien Abduction: Incident in Lake County, Cube, 10 Cloverfield Lane
Psychological
It is truly an ignominy that Psychological horror tends to be underestimated for being misunderstood (or not understood whatsoever).
It is not conventional, not even in the slightlest; do not let that fool you. If approached for knowing and expecting the unexpected, one can find the finest depictions of horror that can be offered. Silent Hill took note and used Jacob's Ladder as its blueprint; that alone makes it up for showing the scope of this subgenre.
Prime Example: Jacob's Ladder
Worth-checking movies: Mother, Get Out, Thesis, Goodnight Mommy, The Shining
Supernatural Horror
It is trully unfortunate that this subgenre, which at its prime was the most prolific and exciting, is now a played out way of depicting horror.
Alongside Slashers, Supernatural horror is the most recognizable; ask almost anyone about horror movies and it is highly likely that what they mentioned is related to it. The life of this subgenre has had its peaks and valleys; from all-dominant in the 60's and 70's to its fall in the 80's and 90's, and its recovery in the past two decades to its relapse in the last few years. Nowadays, there are supernatural movies galore (most of which are rather boring and pointless); nevertheless, from time to time we get to have horror-defining gems. We all expect its triumphant return to form.
Prime Example: Rosemary's Baby
Worth-checking movies: It Follows, The Exorcist, Carrie, Hereditary, The Babadook
Cosmic Horror
The term coined to describe the majority of the body of work produced by the ever present H.P. Lovecraft is what provides the name for this subgenre (a.k.a. Lovecraftian horror).
Cosmic horror is the most underestimated and overlooked in the whole list (and that speaks volumes in a list with Psychological and Folk horror). This may not be difficult to explain taking into account that its focus on the unknown and incomprehensible is what gives it its identity. If approached knowing its modus operandi, you are likely to enjoy some of the most terrifying and interesting movies the genre has produced.
Prime Example: In The Mouth Of Madness
Worth-checking movies: The Lighthouse, Annihilation, The Ritual, The Endless, The Empty Man
Folk Horror
Folk horror is the richest in terms of source material and symbolism. Leaning on folklore and based upon the consequences and effects of religion and the darkness present in human nature, it is, undoubtedly, of the highest consideration in the scare factor.
As folklore varies from place to place, we are before the subgenre with the highest potential in horror. Not really meaningful but worth-mentioning is the fact that I consider it the most ominous and terrifying of them all.
Prime Example: Midsommar
Worth-checking movies: The Wicker Man, The Witch, Onibaba, The Blair Witch Project, The Blood on Satan's Claw
Splatter
Barely making it to the final list, Splatter is quite divisive and controversial. I myself admit that it is the subgenre with the lowest quality out of all the mentioned.
Through cheap violence, simple plots and lots of gore, Splatter wants to gain your attention and repulsion. Why is it here then? Well, when it gets it right, we get game changing movies (The Evil Dead, Saw), extremely amusing films (The Devil's Rejects) and new horror icons (Art The Clown). I just wish Splatter got it right more often than it does.
Prime Example: The Evil Dead
Worth-checking movies: Saw, The Devil's Rejects, Terrifier, Braindead, Planet Terror
A-Horror
I wanted to mention this one as J-Horror due to the fact that, horror-wise, Japanese films are the best outside Europe. Nonetheless, there exist a couple of South Korean and Indian movies that made me change the heading.
Asian horror is, perhaps, the scariest in all of cinema. Because of this, people are often repelled from it. Moreover, the average Asian horror movie possesses the highest quality in the genre (presentation and writing). Once averse to it, I now embrace it as the jewel it is. Just hope everyone could to the same.
Prime Example: Audition
Worth-checking movies: Tetsuo: The Iron Man , Pulse, Cult, A Tale Of Two Sisters, Noroi: The Curse
Giallo
Named after the (popular?) mystery novels in Italy in the 70's, this subgenre, which can be literally translated as Yellow in Italian, tapped into the boost of Slashers and Spaghetti Westerns. Taking into consideration these distinctive characteristics Suspiria has no business in here. I know, but can we take Helena Markos and her coven as a fierce and unstoppable killer? I know you will excuse my choice.
Highly influential in terms of presentation (specially the foundation of what in modern times has been named as Exploitation), Giallo offers incredibly well-executed films by a top tier list of filmmakers. Lucio Fulci, Mario Bava or Dario Argento might be named as greats in horror, not only regarding their precious Gialli films.
Prime Example: Suspiria
Worth-checking movies: Blood and Black Lace, Opera, Deep Red, The House with the Laughing Windows, The Girl Who Knew Too Much
Bonus: Found Footage
I do admit that this one is cheating, but being the biggest Found Footage fanboy that I am I could not leave it outside; well-known is the fact that it is a filming technique and not a proper subgenre.
In spite of that, it is the most amusing and immersive way of experiencing horror. Not only that, basically, you are able to find each one of the aforementioned subgenres in a Found Footage format: all of the V/H/S franchise for Body horror; Behind The Mask for Slasher; Phoenix Forgotten for Sci-fi; Be My Cat: A Film For Anne for Psychological horror; The Fear Footage for Supernatural; The Banshee Chapter for Cosmic horror; The Blair Witch Project for Folk; The Butcher for Splatter; Cult for A-Horror and I do not recall any Gialli films in the format (you may consider Cannibal Holocaust just for being Italian but not for the characteristics it has).
Prime Example: V/H/S 2
Worth-checking movies: Hell House LLC, Lake Mungo, The Monster Project, The Sacrament, M.O.M. (Mothers of Monsters)