The first paragraph of the Wikipedia article (as of April 17, 2013) gives a good, very basic introduction to Hanns Ewers:
“Hanns Heinz Ewers (3 November 1871 in Düsseldorf – 12 June 1943 in Berlin) was a German actor, poet, philosopher, and writer of short stories and novels. While he wrote on a wide range of subjects, he is now known mainly for his works of horror, particularly his trilogy of novels about the adventures of Frank Braun, a character modeled on himself. The best known of these is Alraune (1911).“
The article continues on to describe some of his literary achievements:
“This was followed in 1911 by Alraune, a reworking of the Frankenstein myth, in which Braun collaborates in creating a female homunculus or android by impregnating a prostitute with the semen from an executed murderer. The result is a young woman without morals, who commits numerous monstrous acts. Alraune was influenced by the ideas of the eugenics movement, especially the book Degeneration by Max Nordau. Alraune has been generally well received by historians of the horror genre; Mary Ellen Snodgrass describes Alraune as “Ewers’ decadent masterwork”, Brian Stableford argues Alraune “deserves recognition as the most extreme of all “femme fatale” stories”  and E.F. Bleiler states the scenes in Alraune set in the Berlin underworld as among the best parts of the novel. The novel was filmed several times, most recently by Erich von Stroheim in 1952.
Bleiler notes “Both Alraune and The Sorcerer’s Apprentice are remarkable for the emotion the author can arouse” and that Ewers’ writing is, at its best, “very effective”. However, Bleiler also argues Ewers’ work is marred by “annoying pretentiousness, vulgarity, and a very obtrusive and unpleasant author’s personality”.“
So far I have read only two of Ewers’ short stories: “The Spider”, described as his “most anthologized work”, and “Fairyland”. I will need to read more of his works to be able to speak with some degree of confidence that I know what I am talking about, but my first impression of Ewers’ works is one of disappointment.
I read both works in English (though I speak German with moderate fluency), and his command of composition, organization, language, clarity, and suspense are competent enough, but at least the stories noted above seem to fall apart at having a comprehensible denouement, and in the area of having good taste.
“The Spider” starts off well enough with a great opening paragraph that sets the stage for suspense:
“When the student of medicine, Richard Bracquemont, decided to move
into room #7 of the small Hotel Stevens, Rue Alfred Stevens (Paris 6),
three persons had already hanged themselves from the cross-bar of the
window in that room on three successive Fridays.”
As the story develops, Bracquemont volunteers to work with the police in finding out why the three previous residents killed themselves by reporting what he sees during his stay. He records his observations in a diary. Over the next three or so weeks, Bracquemont begins observing a girl in another room across the street, who constantly spins at an old-fashioned spinning wheel. He begins to be attracted to her, he waves to her, they develop games to play over the distance (mimicking each other, etc.), he becomes infatuated with her, and obsession sets in all the while there are subtle hints of analogies between her and a female spider luring her mate to its death. I will not spoil the ending for you, if you want to read it (I read the version at Project Gutenberg Australia), but I will say that the story seemed rather drawn out and the ending was confusing with no real explanation as to why the story ends as it does. I suppose one could say it was “black magic”, as one critic noted, but there is nothing alluding to black magic anywhere previously in the story. The ending is sort of deus ex machina and very unsatisfying.
“Fairyland” is worse. It’s only virtue is that it is very short. It is the story of a cute little girl on a tramp steamer in Port-au-Prince who is the darling of the crew and who tells them of wonderful monsters she has seen ashore, monsters with enormous heads and limbs and scales. She offers to show them to the crew and the crew agrees to go along wondering what she has found. Not far from the docks, she shows them the local beggars who have enormous limbs from having contracted elephantiasis or scales from leprosy or a similar skin disease. While the crew is obviously overcome with disgust, the little girl prattles on about how cute the monsters are.
I am not one to berate anyone else over a lack of taste, but whoever published this deserved a good horsewhipping for deciding to put this atrocity in the public view. It is one of the more tasteless things I have ever seen. However, I will discourage anyone from reading it. After all, it is a matter of taste and we are dealing with matters of horror.
So far, Ewers is the one author of horror I have been most disappointed by. Still I will read at least a few more of his works before I solidify my opinion. At some point I may read Alraune only because it is his best known work, but from what I have seen of its reviews, it may be a struggle for me to wade through horrors which only the Marquis de Sade would appreciate.
Perhaps Ewers does deserve his accolades. I will only know by exploring his works further. So far though, I am not looking forward to the journey, which I make only out of intellectual curiosity.
There is one interesting sidelight about Ewers for fans of cinematic horror. One reviewer commented somewhere (I forget where) that Alraune was the original inspiration for genetically-mutated femme fatales like the alien in the Species trilogy.