The 40s weren't exactly known for high-quality genre fare, but there are always exceptions, and the premise here sounds interesting. I do rather think the telling here is troubled in at least some measure given instances of lagging pacing, a variable but often lighter tone, and ill-fitting wry humor (from bullying and ignorant police, naturally). On the other hand, those deeply unlikable cops are counterbalanced by the fabulous, combative wit of other characters, and the pacing and occasional tonal issues by tinges of atmosphere that the feature ably fosters. That atmosphere comes to us by way of smart use of lighting, the more haunting of those chords in the music, and Ian Keith's dramatic, imposing performance as the antagonist. It's still true that the horror 'Valley of the zombies' offers is more thematic than it is actualized, yet between Dorrell and Stuart E. McGowan's screenplay and Philip Ford's capable direction, this is sufficiently well made to rise a little bit above the more middling level of some of its contemporaries.
The darker notions in the storytelling and of the accompanying ambience are adjoined with broader airs of mystery as lab workers Terry and Susan seek to discover by themselves the truth surrounding recent murders. Usually I'd criticize the levity in the chief characters' dialogue as unbecoming of the nature of the material, nevermind how they are written (especially as Susan is a woman prone to jumping at her own shadow). I do think that holds true here to no small degree, and for the fact of it the resulting tableau will hold less appeal for genre purists, those who have a hard time engaging with older films, or those who look above all for visceral thrills in their horror. Yet the McGowans gave Robert Livingston and Adrian Booth some genuinely sharp and clever lines to impart as Terry and Susan, and overall I think the picture is just balanced enough so that the touches of comedy, the mystery, and the underlying horror concept all blend together fairly well - a balance which itself is sadly relatively rare in genre flicks from this timeframe.
The art direction is terrific; stunts and effects are modest by most any standards, but appreciable. Even sound effects are employed well, and the cinematography; other minutiae like costume design, hair, and makeup are just swell. The narrative is fundamentally solid, despite the details in its telling that weigh upon it to its detriment, and the same definitely goes for the scene writing. The horror vibes this has to offer may be less robust than in countless other examples among its brethren, yet they are present and meaningful nonetheless; one can easily imagine what 'Valley of the zombies' would look like if it were made at any point from the 60s or 70s onward. What we have here, then, is a movie that's ultimately very well written, and very well made by the standards of its timeframe. If the final product lacks the vibrancy of that genre enthusiasts are accustomed to it's only as a matter of the sensibilities by which such titles were once made, and not a specific failing on the part of anyone here. In fact, though it's no exemplar, I'm inclined to believe that this is one of the better horror films to have been released under the Hays Code.
It's not perfect, but it's duly engrossing, certainly entertaining, and unexpectedly satisfying. That's more than can be said of innumerable features even in all the decades since. Anyone who isn't receptive to the stylings of 40s cinema won't find anything here to change their minds, yet if you're open to all the wide possibilities of what the genre has to offer, there's much more to like here than it may seem at first blush. Don't necessarily go out of your way for 'Valley of the zombies,' but if you do have the chance to watch, this is actually well worth a mere fifty-six minutes of one's time, and I'm pleased to give it a firm recommendation.