"The most merciful thing in the world, I think, is the inability of the human mind to correlate all its contents" 
 This quote from early pages in the book summarizes the all the genres this story imbibes. Its an immensely enjoyable story with the way the mythos is dived into in the very first paragraph and everything else is an exploration of that idea. There is no direct fear inducing factor but it is implied through out the story. The fear of the creature exists in all of us the way the society is going towards its decline. Maybe this creature exists or maybe it doesn't. Lovecraft puts out the notion out there that the downfall of mankind is imminent and this creature is just bidding its time. Its interesting to see that the fear is more psychological than a physiological response to a certain event which makes the story all the more enjoyable. 
 This may not appeal to some audience as it isn't technically a story in narrative style. Its bunch of perspectives put together that makes a grand picture.