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It's best to get into Lovecraft in his non-Cthulhu works.
Lovecraft is one of the first world builders.
There's world building since forever, but it's usually ad-hoc, mismatched, retconned bi-product of just writing a lot of books. Such as comic books, where Batman has several origin stories and Superman has more powers that he no longer uses than we can count.
Premeditated world building, like Lovecraft was doing, was pretty groundbreaking. Along with texts like LOTR, it changed how we think about genre fiction. It hasn't aged well, and IMHO, unless you're a teenager, it's not worth getting into, but I disagree that Lovecraft is overrated.