And Then There's John Bellairs
So, while I think Lovecraft is interesting as a mythmaker but not a v. good writer, and Clark Ashton Smith brilliant but admittedly an acquired taste, I think the late John Bellairs, at his best (i.e., The Face in the Frost) can best even C.A.S.Yes, lo to those who first read Face during his or her youth on a rainy, windy night.
Bellairs' vocabulary is much simpler, but he was a master of using detail to evoke a sense of nightmares. And I mean that literally: I've had nightmares after reading Bellairs, which has never been the case with HPL or even CAS.
He then goes to quote a few memorable passages from chapter five. That's the one with the forest - you remember. If not, don't just take our advice, take Ratelif's as well.