The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents. We live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. The sciences, each straining in its own direction, have hitherto harmed us little; but some day the piecing together of dissociated knowledge will open up such terrifying vistas of reality, and of our frightful position therein, that we shall either go mad from the revelation or flee from the deadly light into the peace and safety of a new dark age.And while I have great sympathy for the purists and pedants who correctly point out that Lovecraft himself never used the phrase "Cthulhu Mythos" to describe his stories -- it's a coinage of August Derleth, whom I think often gets a disproportionately bad rap -- there's a sense in which it's a far better term than Lovecraft's own suggestion of "Yog-Sothothery," for "Cthulhu Mythos" recognizes the centrality of "The Call of Cthulhu" in enunciating the philosophy behind his cosmic tales.
The story itself is dense and complex, consisting of multiple, layered narratives that each contribute to the mounting horror of the piece. Subtitled "Found Among the Papers of the Late Francis Wayland Thurston, of Boston," "The Call of Cthulhu" is thus ostensibly a text written by the aforementioned Thurston after his investigation into the death of his great uncle, George Gammell Angell, who was a professor of Semitic languages at Brown University. Thurston's text itself consists of multiple, nested sub-texts assembled by Angell from the accounts of others. Consequently, "The Call of Cthulhu" is at times a challenging read, the thread of its narrative easy to loose amidst Lovecraft's moving forward and backward in time and place.
Nevertheless, the narrative that emerges from "The Call of Cthulhu" is a compelling one: over the span of many years, across the globe, there are signs -- dreams, cults, unexplained events -- that something is stirring, something that spells the doom of mankind, though not out of malice, let alone evil, but simply because man and all his works are but nothing in the cosmic scheme. It is this singular point that Lovecraft makes clear again and again throughout "The Call of Cthulhu" and it is the true source of its horror, not the monstrous octopus-headed Great Old One that rises at its climax in the South Pacific. Equally noteworthy, I think, is Lovecraft's prose in this story. He has largely cast off the sometimes-stilted, pseudo-Poe voice of his early tales and embraced an almost clinical approach that lulls the reader into a "detached" state of mind that leaves him ill-prepared for Lovecraft's stylistic shift late in the story toward impassioned, even frenzied prose-poetry.
"The Call of Cthulhu" is a landmark both in HPL's evolution as a writer and in the evolution of literary horror. Considering both its age and the degree to which it has been imitated over the later 80+ years, it's frankly amazing how well it stands up. If there was ever any doubt that H.P. Lovecraft is a writer of consequence, this story ought to banish such notions completely.