I love Lovecraft for the prose. Just like Robert E Howard and Clarke Ashton Smith--all three self-made provincial poets from nowhere, and their dense, grotesque prose hums with energy and very frequently one sentence is worth 50 pages of modern writers in terms of impact. I re-read these people every year.
I also very much enjoy submerging into the British Elder Gods branch of Chambers, Machen, and Blackwood. Especially Blackwood.
But if I were to pick one thing from all those pre-WWII geniuses, I'd pick a Lovecraft book--The Dream Quest one. I discovered it in my late twenties and was floored--a thin novella which was mightier than LOTR. Later I saw Patrick Rothfuss put it at number 1 in his list of best fantasy ever, and I was glad someone else shares this sentiment.
I think Lovecraft doesn't write wrong. Everyone else writes wrong. And Tolstoy doesn't write boring books. Anna Karenina only seems boring to...well, let's not say boring people, but rather people in a more shallow period of their lives, IMO. God knows I've had my share of those periods.
Of course, the short American book full of people spitting out barely comprehensible lines while lighting one cigarette after another can also be wonderful, for example Hammett's contributions to the field.
A good pulp, or better yet, a glorious pulp, is a transcendental experience, and Lovecraft, just like Hammett, in his different way, is glorious pulp. And in our time of a potential resurgence of 'pulp' in the compressed, snappy version, thanks to the rise of e-books mainly, it makes total sense to re-read the old masters. Because sometimes a fight on the street is best described in Hammettian terms and a mystical experience in the woods is best described in Blackwoodian terms, and an out-f body experience with alien entities--in Lovecraftian terms--and it doesn't matter if all this takes place in a time of iphones and spy drones.