Oddly, I first heard of Blackwood in an old Black Sabbath interview. Bassist Geezer Butler mentioned that a lot of his lyrical inspiration came from horror films and authors like Algernon Blackwood. Naturally, I had to seek out the fellow's books. Fortunately, my father and grandfather both seem to have had a solid streak of appreciation for good horror, because I burrowed around through the shelves their houses and found two compilations of Blackwood's short stories - one published in the 1920s, the other in the 1970s.
Blackwood is, as others have mentioned, a more consistently readable stylist than Smith. His stories are often less in-your-face horror as they are about the supernatural and occult finding its way into real life. In this aspect, I see his approach to horror as reflecting the 'spirit' fad of his times, although with a greater conviction and depth than many Victorian spiritualists actually posessed. Some of my favourite Blackwood stories are about the psychic investigator, John Silence.
Blackwood often set his stories in outdoor settings, against forests and swamps or in hilly regions. He excels as a descriptive writer, giving you a vivid sense of place. This earthy naturalism serves as an especially effective underpinning for the supernatural elements of his stories.
HP Lovecraft, never reticent in speaking of the many excellent writers who shaped his own vision has this to say about Blackwood in his essay 'Supernatural Horror in Literature:
"Less intense than Machen in delieating the extremes of stark fear, yet infinitely more closely wedded to the idea of an unreal world constantly pressing upon ours is the inspired and prolific Algernon Blackwood, amidst whose voluminous and uneven work may be found some of the finest spectral literature of this or any age. Of the quality of Mr. Blackwood's genius there can be no dispute; for no one has even approached the skill, seriousness, and minute fidelity with which he records the overtones of strangeness in ordinary things and experiences, or the preternatural insight with which he builds up detail by detail the complete sensations and perceptions leading from reality into supernormal life or vision. Without notable command of the poetic witchery of mere words, he is the one absolute and unquestioned master of weird atmosphere; and can evoke what amounts almost to a story from a simple fragment of humourless psychological description. Above all others he understands how fully some sensitive minds dwell forever on the borderland of dream, and how relatively slight is the distinction betwixt those images formed from actual objects and those excited by the play of the imagination."
I admire Clark Ashton Smith's imagination and his way with words - there's no denying that he was a man deeply in love with language and its rhythms, and took the affair to extremes at times. I like his Averoigne tales a lot, although the Zothique tales have some seriously memorable weird scenes and characters in them. Many of them read like incomplete fragments from lost manuscripts chroncling some world that never existed - at least, that's how I like to think of them. It's very hard to read several of his stories in succesion and indeed, doing so is probably a disservice to both Smith and yourself. It's best to savour them at the rate of one or two a month, much as his original readers would have, in the monthly pulp magazines. Too many of them at a time and the stories can start seeming like unintentional self-parody.
Smith was also a poet, painter and sculptor. Many of his sculptures would not be out of place as the 'accursed artifact' of a Lovecraftian tale. They posess a raw, primitive power that is very different from the polished pleasures of his prose and poetry.
Nyctalops is one of my favourite poems by Smith. It almost seems like a paean to all the strange visions that Smith and his fellow visionaries of the Weird Tales era dreamed up.