The Great God Pan's implied sexuality caused a scandal upon its original release and hurt Machen's reputation as an author.
Reviewing the novella for the magazine Literary News, Richard Henry Stoddard criticised the story as "too morbid to be the production of a healthy mind".
The art critic Harry Quilter's review of the book, titled "The Gospel of Intensity", and published in The Contemporary Review in June 1895, was even more harsh.
Quilter declared: "'The Great God Pan' is, I have no hesitation in saying, a perfectly abominable story, in which the author has spared no endeavor to suggest loathsomeness and horror which he describes as beyond the reach of words."
Quilter warned that Machen's books were a dangerous threat to the entire British public and that they would destroy readers' sanities and senses of morality.
Quilter went on to attack the story's publisher, John Lane, as well as Machen himself: "Why should he be allowed, for the sake of a few miserable pounds, to cast into our midst these monstrous creations of his diseased brain?"
Quilter added that works of fiction like Machen's should be unanimously condemned by literary critics and newspapers: "If the Press was so disposed it could stamp out such art and fiction in a few months: And that disposition must be acquired, must even be enforced."
He was particularly harsh in his denunciation of sexual ambiguity and polymorphous androgyny in the book.
He expressed revulsion at Machen's description of Helen's sex changing immediately before her death and concluded his review with a comment of distaste regarding the "nasty little naked figure of dubious sex and humanity with which Mr. Aubrey Beardsley has prefaced the story".
A positive appraisal of the novella came from Oscar Wilde, who called it "un succès fou."

Machen's literary reputation was re-evaluated in the 1920s and The Great God Pan has since attained the reputation of a horror masterpiece.
In "Supernatural Horror in Literature" (1926; revised 1933), H. P. Lovecraft praised the story, saying: "No one could begin to describe the cumulative suspense and ultimate horror with which every paragraph abounds"; he added that "the sensitive reader" reaches the end with "an appreciative shudder".
Lovecraft also noted, however, that "melodrama is undeniably present, and coincidence is stretched to a length which appears absurd upon analysis".
Bennett Cerf described the story as a "masterpiece".
Brian Stableford stated that The Great God Pan is "the archetypal Decadent horror story" and described the story as "highly original".
Stephen King referred to it as "one of the best horror stories ever written.
Maybe the best in the English language."
The Washington Post's Elizabeth Hand deemed it "one of the greatest supernatural tales ever written".
Black Gate's Matthew David Surridge said that The Great God Pan is "a fascinating, troubling story, and, for all its influence, not like much else than I can think of.
It's not simple, and yet it's effective, more so than can easily be explained."

Some commentary on The Great God Pan has focused on its portrayal of women.
Surridge sees the novella as expressing a fear of women even though the ultimate source of horror in the story is a male deity.
The Encyclopedia of Science Fiction says that Helen's "metamorphosis...remains one of the most dramatically horrible and misogynistic in fiction".
Helen never speaks in the book; according to Victoria Margree and Bryony Randall in Victorian Gothic: An Edinburgh Companion, "The silence of the central female character is part of the text's misogyny, but also part of its narrative effect."
Margree and Randall also view Helen's fate as a punishment for her sexual impropriety.
Dennis Denisoff connects Machen's tendency to make his empowered female characters "sexually monstrous" to his criticisms of authors who discussed the subject of women's rights.
James Machin defends Machen and The Great God Pan from charges from misogyny on the grounds that the male protagonist of Machen's story "The Novel of the White Powder" (1895) disintegrates in
The Great God Pan's implied sexuality caused a scandal upon its original release and hurt Machen's reputation as an author. Reviewing the novella for the magazine Literary News, Richard Henry Stoddard criticised the story as "too morbid to be the production of a healthy mind". The art critic Harry Quilter's review of the book, titled "The Gospel of Intensity", and published in The Contemporary Review in June 1895, was even more harsh. Quilter declared: "'The Great God Pan' is, I have no hesitation in saying, a perfectly abominable story, in which the author has spared no endeavor to suggest loathsomeness and horror which he describes as beyond the reach of words." Quilter warned that Machen's books were a dangerous threat to the entire British public and that they would destroy readers' sanities and senses of morality. Quilter went on to attack the story's publisher, John Lane, as well as Machen himself: "Why should he be allowed, for the sake of a few miserable pounds, to cast into our midst these monstrous creations of his diseased brain?" Quilter added that works of fiction like Machen's should be unanimously condemned by literary critics and newspapers: "If the Press was so disposed it could stamp out such art and fiction in a few months: And that disposition must be acquired, must even be enforced." He was particularly harsh in his denunciation of sexual ambiguity and polymorphous androgyny in the book. He expressed revulsion at Machen's description of Helen's sex changing immediately before her death and concluded his review with a comment of distaste regarding the "nasty little naked figure of dubious sex and humanity with which Mr. Aubrey Beardsley has prefaced the story". A positive appraisal of the novella came from Oscar Wilde, who called it "un succès fou."
Machen's literary reputation was re-evaluated in the 1920s and The Great God Pan has since attained the reputation of a horror masterpiece. In "Supernatural Horror in Literature" (1926; revised 1933), H. P. Lovecraft praised the story, saying: "No one could begin to describe the cumulative suspense and ultimate horror with which every paragraph abounds"; he added that "the sensitive reader" reaches the end with "an appreciative shudder". Lovecraft also noted, however, that "melodrama is undeniably present, and coincidence is stretched to a length which appears absurd upon analysis". Bennett Cerf described the story as a "masterpiece". Brian Stableford stated that The Great God Pan is "the archetypal Decadent horror story" and described the story as "highly original". Stephen King referred to it as "one of the best horror stories ever written. Maybe the best in the English language." The Washington Post's Elizabeth Hand deemed it "one of the greatest supernatural tales ever written". Black Gate's Matthew David Surridge said that The Great God Pan is "a fascinating, troubling story, and, for all its influence, not like much else than I can think of. It's not simple, and yet it's effective, more so than can easily be explained."
Some commentary on The Great God Pan has focused on its portrayal of women. Surridge sees the novella as expressing a fear of women even though the ultimate source of horror in the story is a male deity. The Encyclopedia of Science Fiction says that Helen's "metamorphosis...remains one of the most dramatically horrible and misogynistic in fiction". Helen never speaks in the book; according to Victoria Margree and Bryony Randall in Victorian Gothic: An Edinburgh Companion, "The silence of the central female character is part of the text's misogyny, but also part of its narrative effect." Margree and Randall also view Helen's fate as a punishment for her sexual impropriety. Dennis Denisoff connects Machen's tendency to make his empowered female characters "sexually monstrous" to his criticisms of authors who discussed the subject of women's rights. James Machin defends Machen and The Great God Pan from charges from misogyny on the grounds that the male protagonist of Machen's story "The Novel of the White Powder" (1895) disintegrates in
The Great God Pan