Howard (and for that matter some other "pulp writers") never got the credit they were due in their lives. It was and you hit why on the head, they were "pulp" writers and (so called) "reviewers" felt comfortable snubbing and ignoring them without even consideration. Howard has depths that were not spoted in his own time except by a few. The same can be said to some extent of Lovecraft.
To some extent, yes... but not to the same degree, by any means. Even during or shortly after his lifetime, he had his admirers amongst the literati: Professor Thomas Ollive Mabbott, the noted Poe scholar, praised Lovecraft's work on more than one occasion (including giving him credit for being a genuine Poe scholar, as the one who had solved two long-standing riddles in that particular field -- the location of Mount Yaanek and the reading of "The Fall of the House of Usher" which realized that "a brother, his twin sister, and their incredibly ancient house all shar[ed] a single soul and [met] one common dissolution at the same moment"); Stephen VincentBenét too, according to his brother William, held Lovecraft's work in high esteem. Such was not the case with Howard. It was chiefly the harsh critique by Edmund Wilson, the then-dean of American criticism (and, on the whole, rightly so), combined with August Derleth's complete misreading and promulgation of a therefore distorted version of Lovecraft's work, which caused more damage to Lovecraft than anything else. After all, several of his stories had been picked for the O'Brien lists as among the better short stories of their respective years, and several publishing firms had expressed an interest in seeing a novel from his pen.
As for the "(so-called) reviewers" -- well, they were reviewers, not so-called; whether they were good or not is a separate matter; many were, they were just imbued enough in the more classical tradition to find Howard's faults more grating than his virtues were pleasing; and yes, there was a strong resistance to the pulps (often with good reason). But a fair amount of Howard's work came in for criticism even from his fellow pulp writers; Fletcher Pratt, for example, had short shrift for REH, while Pratt's collaborator, L. Sprague de Camp, felt he was one of the shining lights of the weird and adventure pulps.
Part of the problem is that Howard often wrote so much, in such haste, that his writing can get rather sloppy. Poor sentence structure, run-on sentences galore, excessive coloring (even for the type of tale he was telling) tending toward self-parody, and just flat-out klutziness now and again. And he did have a lot of repetition of ideas, motifs, incidents, and even phrasing among his works (how many "killer apes" did Conan go up against, for example? then add in the ones El Borak and his other characters faced, and you begin to see a paucity of creativity in this area... and so on).
And before I have a horde of Howard's true believers descend on my head, please recall that I've been a fan of Howard's work for the better part of 40 years now, and still enjoy it immensely. It is just that I also read his work without the rose-colored glasses many (not all) do, and realize his faults
and accept them as part of the writer he was, due to circumstance and personality. With all his faults, Howard did write with a verve and passion which raises a rather large amount of his work far above all those faults put together, and the fantasy and adventure fields would have been much poorer without him.
I get annoyed when I see the term "thud and blunder" used in connection with herioc fantasy in general and REH in particular.
Yes, the term has been overused, but in the case of some writers, it is unfortunately well deserved. There was a tremendous amount of ephemeral trash written in this subgenre, most of it quite deservedly forgotten today. It was simply badly written: clumsy, stereotypical, hackneyed, and without the tiniest scintilla of integrity or attempt at verisimilitude or even proper story -- let alone sentence -- construction. Adelbert Kline was a good example -- a lovely man, and he certainly helped fill the pages of a number of magazines, but the majority of his work is pure dross. At his best, he was like a very badly xeroxed copy of E. R. Burroughs; at his worst, he was frankly unreadable by anyone with any critical sensibilities at all.
Howard was not
entirely exempt from this, but it was much less frequent than some have contended. And one should read Howard a little more carefully, as he did sometimes indulge in deliberate parody; as in "The Jewels of Gwahlur"/"The Servants of Bit-Yakin", where, when Conan shows up to the relief of the (chained and) imprisoned Muriella, she "madea spasmodic effort to go into the usual clinch" (i.e., hysterically wrapping herself around her rescuer -- including his sword-arm, one suspects -- thus rather hampering his effectiveness in that role).
And, yes, at his best -- which was not that seldom -- Howard touched emotional depths and complex sets of emotional keys that gave his work genuine power. There is genuine pathos to much of his work; a poetic sense of, as de Camp phrased it, the underlying tragedy of life; and no small amount of beauty and even the numinous at times. Some passages in his prose work is sheer poetry; and much of his verse is remarkably good.