There a few ways to interpret what is 'horror' and what isn't, everyone can have their own interpretation. Each of these have elements in them that one can consider horror and are just a few examples. (I just copied the list from an earlier post I made and added synopsis/reviews). Sorry if you've seen a few, many, or all of these already. That goes to anyone else looking at this list.
Ghost Hound -
Though seeming small and modest, Suiten is not a picturesque place for a vacation, unless it is from the “Unseen World”. However, the Unseen World is no mere copy of the real Apparent World. The Unseen World is the home of ghosts, but changes are now allowing the souls of the dead to pass over into the Apparent World, with unpredictable effects. ~ Ultimately rather conventional in content, it is consistently unconventional in execution. Creating a hanging sense of dread, a portentous quiet that threatens more than any maelstrom could. It claws its way to ascendancy. [Bits taken from MyAnimeList and Anime News Network DVD review]
Kakurenbo: Hide & Seek - Among the ruins of the city, there is a game only children can play. But whenever children play this game, one by one they would disappear into the blinds of the buildings. A game of hide-and-seek; ready or not..... here they come. ~ Kakurenbo is completely shot in dark or overcast scenes with only flickering lights, neon signs, and the occasional glowing pair of eyes. Silence is definitely golden. [Bits taken from MyAnimeList and Anime News Network DVD review]
Mermaid Forest
Perfect Blue
Jin-Roh: Wolf Brigade
Gantz -
A word of warning: Gantz is not for the faint-hearted, but neither is it as simple as it looks. Gore, rape, and violence is rampant, as are portrayals of greed, violence, and all the ugliness that one sees in society. There is no salvation, peace, nor god waiting to receive you into their care. This is the game. Enjoy being dead. ~ The first piece is a discordant dissection of the human mind, examining the private thoughts and emotions that run through the heads of society. The second piece is an alien-hunting game. Great visuals, heavy doses of graphic content, exciting action scenes, and, most importantly, credible portrayals of flawed central characters. [Bits taken from MyAnimeList and Anime News Network DVD review]
Monster -
One critical decision - whether to save the life of a young child or that of the town's mayor. Dr. Tenma’s world is turned upside down by his decision leading to the loss of everything he previously had. A doctor is taught to believe that all life is equal; however, when a series of murders occur in the vicinity of Dr. Tenma, all of the evidence pointing to the young child who he saved, Tenma’s beliefs are shaken. ~ A self-proclaimed exploration into how human beings turn and are turned into monsters, an end that goes out with a whimper, not a bang…more's the pity. The whimper in question is a long, anguished wail of agony. [Bits taken from MyAnimeList and Anime News Network DVD review]
Elfen Lied -
Captured and isolated in laboratories by the government, the Diclonius, a mutated homosapien that is said to be selected by God and will eventually become the destruction of mankind, possess two horns on their heads and have a "sixth sense" which gives them telekinetic abilities. ~ A horror series of exceptional merit, this isn't a series that children should be anywhere near, and it's not for the prudish, squeamish, or anyone else that doesn't have a very high tolerance for nudity, extreme graphic violence, or general cruelty. [Bits taken from MyAnimeList and Anime News Network DVD review]
Hell Girl
Le Portrait de Petite Cossette
Blood+ -
Throughout the passage of time and the shifts in backgrounds, a particular war continues to leave its mark on history, extending its influence into the modern world. Monsters known as Chiropterans who feed on the blood of the living and an organisation known as the "Red Shield", formed to track down these monsters and exterminate them. Otonashi Saya has no recollections of her past life but her present one will be destroyed by an event that will lead her to her destined fate. ~ Inhuman swordfights in the hotels and harbors of Paris, gritty confrontations on the fog-shrouded streets of London, desperate impromptu struggles in the picturesque English countryside, aerial battles in the dark skies of New York. Cold-blooded tragedies. Vampirism. In its own whip-lashing start-and-stop way, Blood + is every bit as bloody entertaining and sneakily addictive. [Bits taken from MyAnimeList and Anime News Network DVD review]
Another
Shiki -
In Sotoba, a peaceful and quiet village with a population of 1300 people, a series of bizarre deaths begin to occur. At the same time, a strange family moves into a long abandoned mansion in the region. Then, the fashionable Shimizu Megumi goes missing and the entire village goes out in search for her. ~ Shiki is simply taking the time to look at a textbook vampire infestation from every angle. The shifting range of colors sets the series' dark mood, so does the music, adding to the unease. Dark and gloomy. [Bits taken from MyAnimeList and Anime News Network DVD review]
Texhnolyze -
In a man-made underground society, descendants of a banished generation vie for control of the crumbling city of Lux. As Ichise is drawn deeper into a war for territorial control of the city, he learns of his possible future from the young girl prophet Ran, who guides him from the shadows in his darkest times. With the explosion of the warfare, Ichise must uncover the truth about Lux and fight for his survival as he realizes his destiny. ~ Presenting nothing in its twenty-two episodes that is happy or nice or emotionally enriching it very much intends to upset and alienate. It is one long, violent spiral into utter hopelessness. [Bits taken from MyAnimeList and Anime News Network DVD review]
Serial Experiments Lain -
The sudden suicide of a schoolmate, and a number of strange occurrences, conspire to pull Lain Iwakura into the world of the Wired, where she gradually learns that nothing is what it seems to be... not even Lain herself. ~ Slow, surreal, layered with symbolism and a vague, wandering non-story, all employed toward exploring the boundary between what is real and what is Wired. Every scene, every action feels significant, however little sense it might make, and everywhere there are subtle hints and allusions to... something. [Bits taken from MyAnimeList and Animeworld Anime Review]
Hellsing -
Hellsing, a secret organization of the British government, has long been battling supernatural threats to keep the people safe from creatures of the night. The Hellsing Organization must face not only regular ghouls and vampires, but a rivaling secret organization from the Vatican, and Millennium, an enigmatic group of madmen spawned by a certain war over 50 years ago. A bloody battle between monsters is about to begin, the dead are dancing, and all hell is singing... ~ Vampires, gun fetishes, massive gore, casual blasphemy, Nazis. And from there, if you're the least bit susceptible to this kind of thing, there's no going back. [Bits taken from MyAnimeList and Anime News Network review]
Boogiepop Phantom
I kind of didn't piece together all of them (a basic synopsis and review that is), forgive me on that. I'll put the rest in later.