There's something to be said for the limited location thriller. A claustrophobic feeling can be built up in one or two locations that can't be achieved by a sprawling narrative that spans the world. There are examples of this sub-genre that succeed quite well, and those that simply don't work. All the Devil's Aliens a/k/a Devils in the Darkness falls somewhere between those two extremes.
Mike (David Gries) is studying for his med school entrance exams, and wants a job that will leave him plenty of time to study. He thinks he's found just the one when the home health agency assigns him to help Mr. Pinborough (Joseph Scott Anthony). Pinborough is a wealthy recluse who lives in his secluded house in the woods, and requires constant care. Mike's job will simply to assist the head caregiver Robin (Lisa Mueller) by preparing meals, doing maintenance, etc.
Mike's arrival is spoiled a bit when he meets the woman who he is replacing, as she storms out, with her last shift only half over, a bruise on her face, pausing to vomit before driving away ranting. But that's okay. He knows the old guy is a bit of an eccentric, and Robin has been working as his caregiver for years, so it will be fine.
But things don't stay fine for long. There are strange noises, and dark figures moving about in the house, just out of sight. Robin tells him that everyone who works there sees shadows on their first day. Pinborough has very strict rules, mostly about quiet and order, though another one is that no male is allowed to enter the home, so Mike has to make sure to remain silent almost all the time. Things start to get weirder as he learns more of the history of the old man, and even weirder still when Robin disappears.
The producers of All the Devil's Aliens show a sharp aptitude for creating and maintaining suspense. Pinborough is almost always audible over the baby monitor that his caregivers keep in the kitchen, and his meandering monologues, insults and incomprehensible rants create an eerie feeling of disquiet. Quite a few really good jump scares are peppered throughout as well, keeping the audience on edge, waiting for the next one. They also wisely keep the creatures out of full view, using only glimpses and quick looks.
However, the pacing of the film is abominably slow. A number of scenes continue on many minutes past the point of usefulness. Sure, they might help build the atmosphere, but at the expense of boring the audience, which isn't a good tradeoff. In particular, the scene where Mike repeats some variation of "Where is Robin?" a dozen times just grows tedious, and it should have been the emotional apex of the movie. All the Devil's Aliens could easily have been trimmed by twenty minutes without losing any context or understanding of what was going on.
All other aspects of the film are either good or good enough. The performances are solid, the effects better than decent (though there is one, which can't be described for fear of spoilers, that is cheesier than it should have been, but that's a hazard of low budget filmmaking), the sets, lighting, etc. are all competent. This could have been a firecracker of a small thriller, if not for the deadly slow pace. Regardless, there's a lot to like, especially if the viewer is a fan of films with very low funding, of which this is a pretty good exemplar. Recommended, with some reservations.