I first learned about HP Lovecraft, and the Cthulu mythology that his books and short stories generated, when I was 18, in 1997. I imagine that as a science-fiction fan, I had probably read the name in passing before then, but in the days before the internet and instant information access, it was probably just a name I had read in passing. But when I was 18, living in Portland just as it was becoming "Portland", I started hearing about Lovecraft regularly. A friend had suggested the Illuminatus! Trilogy to me, and it referred to the Cthulu mythos. Also, being in downtown Portland, I was now close to many independent movie theaters, and I saw posters for the HP Lovecraft Film Festival. Some of my friends, edgy teens of 1997, started making references to HP Lovecraft. So, following this trend, I went down to the Multnomah County Library and checked out a Lovecraft story collection, and read it, and got to the literary core of the phenomena. As far as Lovecraft as a writer, I agree with a lot of people: his ideas were groundbreaking, he truly developed his atmosphere, but his prose could be overly turgid, and his characters were mostly there for the sake of the plot.
But whatever my reaction to Lovecraft, whether he was great, terrible, or maybe both, the point is that I didn't read Lovecraft without knowing that I was reading Lovecraft. And for everyone I have met who has read Lovecraft, it is the same story: no one just happened to be in a library, find a Lovecraft book and decided to take it home and automatically loved it. Every reader of Lovecraft has been exposed to the cachet of Lovecraft's work, the knowledge that these works are important for the development of horror, that they are referenced and used in other forms of pop culture, the words of praise of a writer like Stephen King. Often people who are interested in Lovecraft, or who use the symbols of Lovecraft, aren't even familiar with the source material. In other words, Lovecraft as a phenomenon has escaped Lovecraft's work, which are often difficult to access.
None of this means that Lovecraft is bad, or that Lovecraft is only a trend or a meme. But it does mean that it is difficult from a lot of fantasy, science-fiction or horror. With The Lord of the Rings or Star Trek, young people pick them up by osmosis, or by coincidence, and start reading or viewing, and the original pleasure of the viewing or reading experience lets them become interested until they become devotees of the mythology. But with Lovecraft, the original impulse is usually that the material is considered esoteric, and to gain the cachet of having read it. And part of this is due to the unique nature of Lovecraft's prose and subject matter: it is impossible to read Lovecraft without being constantly reminded that you are reading Lovecraft.
So imagine a world where "Cthulu" had never become a thing, where Lovecraft was just a name known by a few historians of science-fiction, where there had never been roleplaying games or plush dolls, where elements of the Lovecraft mythos had never been incorporated into things as diverse as Babylon 5, Buffy the Vampire Slayer and Homestuck? Suppose someone came across an HP Lovecraft book or short story, and read it with total naivete? What would the reader's reaction be? Would it be "This is a work of genius!" or would it just be a quizzical shrug at an unusual period piece? My guess is that for most readers, it would tend towards the second. Of course, this is perhaps an unfair standard: many works in horror, science-fiction and fantasy would be impossible to evaluate outside the active role of the fans in constructing their importance. However, for HP Lovecraft, a man who was seen as disagreeable and obscure in his own time, his continued popularity a century later seems to be as much about the recursive celebration of Lovecraft as a phenomenon, than of his writing on its own.