In the middle of a discussion on the RPGSite about what rules would work best with Lovecraft's Dreamlands, I had a little brainstorm: a not completely accurate, but easy to understand, definition of a weird tale would be "like a Twilight Zone story". You introduce a character or three, they experience some strange stuff, and then there's a final weird or horrific twist at the end. Theoretically, a weird tale doesn't have to follow that pattern, but a lot of it did. And there's this branch of weird tale that borders on swords & sorcery that is basically "like a Twilight Zone story set in pre-industrial times". A lot of Clark Ashton Smith's Zothique, Averoigne, Commoriom, and Poseidonis stories fit that description, and so do Lovecraft's early Dreamlands stories, with "The Dream-Quest of Unknown Kadath" still fitting the pattern somewhat, but drifting the farthest towards traditional swords & sorcery or picaresque. Robert E. Howard preferred a more two-fisted tales approach, but he did some that fit this weird fantasy mode, particularly some Solomon Kane stories. You even have a few shorter Fafhrd and Grey Mouser stories that fit that mode, too, and many of Zelazny's Dilvish stories, and the Traveller in Black stories (I think those were James Blish, but I forget.)
And I think the key to distinguishing certain RPG playstyles from certain others is that some old school fantasy wound up more like "pseudo-medieval Twilight Zone" instead of "Tolkien and his imitators".
But thinking about this, especially as to how it relates to the Dreamlands, only reminds me that I ought to use more of a Dreamlands feel in my own games. In particular, the way every little geographical feature or city has some unique, surreal feature, like the city of Thran refusing access to anyone who cannot describe three dreams beyond belief, or the singing river of Oukrianos, or Ulthar, where no one is permitted to kill a cat.