If anyone's made a really good Lovecraft movie, I'm not yet aware of it. It isn't this very '60s Corman flick, which stars an amazingly young Dean Stockwell as the creepy villain and Sandra Dee as the college girl he enthralls for dark purposes.
Through Netflix I saw a far superior, though still not great, retro-silent indie entitled Call of Cthulhu, but this was many years ago and all I remember was that (1) it was kind of slow initially, making a valiant effort to build suspense despite budget and acting limitations and (2) the big reveal of Cthulhu was disappointing. Of course, there's also Re-Animator, but I view it as more in the Evil Dead league than truly Lovecraftian.
If I didn't know better, I would argue that Lovecraft is inherently unfilmable. The terror of the unknown is so foundational to Lovecraft's good stories that movie versions, dependent as they tend to be on visuals, would seem unable to fully succeed at the task of adaptation.
I know better because (apart from the danger of calling anything "unfilmable," as Peter Jackson showed us) there are plenty of truly effective, truly terrifying visual interpretations of Lovecraftian horrors out there, from fan art to the grisly 3rd edition Fiend Folio. To its credit, The Dunwich Horror restrains itself from showing too much of the titular horror—but even the one solid glimpse we get at the end proves to be too much; no amount of flashy late-sixties editing can conceal the Cormanesqueness of the cheap Yog-Sothoth model.
The Dunwich Horror also stars Ed Begley Sr., who slightly resembled Gene Roddenberry, and Talia Shire (Coppola back then), who intensely resembled Mia Sara. But the main point of interest here is Stockwell, whose subtle creepiness as seen in Ron Moore's BSG is turned up to eleven in his role as the young Whateley. (Nobody else in the film really seems to be trying very hard.) Fans of Stockwell's other work may at least find his scenes interesting enough to pay attention to. And yes, there is a scene with a cigar in it, so you may prepare your Quantum Leap riffs in advance.
Otherwise, you'll know what to expect from the very start, even before Corman's name appears—you see, this is an American International Picture. My mental checklist was as follows:
The only other thing I thought we'd get, a scene of dancing women filled with icky sexual undertones, was omitted—but in its place, a timely Dirty Hippie Rape Dream and, later, more buttock-clenching than even Tommy Wiseau would find appropriate. This can't have been a pleasant shoot, and I just hope the cast party was amply supplied with hard liquor.
As one might hope from American International and Corman, the riffability rating is quite high here (e.g.: the professor's strangely pleasant interactions with Whateley after telling him "No you can't BORROW the NECRONOMICON"; the cute head-horn-thing Whateley does with his hands during the summoning). Beyond that, The Dunwich Horror's not really worthwhile except as a strange little curiosity. I suspect it wouldn't even be recommended by Lovecraft completists (of whom I am pleased to say I personally know not a one).
Star Score: 1.5 out of 5