The highest praise I can give is that one could put "The Whisperer in Darkness" on a double bill with "Them!" or "It Came from Beneath the Sea" and it wouldn't feel at all out of place. Watching it for the first time is like discovering a "lost" monster movie classic.
While a low-budget affair with a cast of unknown actors, it transcends its fan film origins and achieves the look of a studio production. The lighting is especially striking, with faces divided by stark shadows.
My only beef is that if this is meant to represent a film released in 1931--the publication date of the novella--it looks and sounds *too* good. Consider that this is the same year that both "Dracula" and "Frankenstein" were released.
"Dracula" has no music outside of a brief snippet of "Swan Lake," and "Frankenstein" has only a few minutes of music composed for the film, but "Whisperer" has a full orchestral score under the entire film.
In general, the movie looks more like something from the late '40s or '50s. That's not really a complaint; again, this is like suddenly learning that a hitherto unknown '50s monster movie has been unearthed.
Both of the HPLHS feature films are excellent, both as productions and as HPL adaptations. Hope that they do a third movie one of these days.