I disagree with a few of the online critics that have reviewed this movie. While they cite likely plot inspirations from sources like Scanners, and Aliens, and Event Horizon, I would instead point to movies like The Power. In that 1968 movie (starring George Hamilton), members of a research group are killed off, one by one, through telekinesis, by someone within the group. Justin Dix, the director of Crawlspace (this is his first full-length movie), sort of uses the same scenario, just not as straightforward or as suspenseful.
Being a special effects supervisor, his direction perks up when the effects come into play, but you do notice a difference between those moments and moments without special effects. The dramatic interactions drag on a little too long, the recriminations and rebukes come a little too easily and are a little too volatile, and having an elite military unit, highly trained for special ops, so easily revert to behaviors usually exhibited by mercenaries is lazy scripting. So is having big guys squeezing through narrow air vents, that perennial movie and television trope that trims budgets and expediently moves people from point-here to point-there.
But this movie is called Crawlspace so the air vents make more sense here; and Dix, for his first go at a complete story does a competent job of telling and showing it. And there's a killer gorilla; in my playbook you can never go wrong when you toss in a killer gorilla. What's missing from Crawlspace is more surprises like that, and naming the mysterious woman "Eve" (Amber Clayton), who has amnesia and a nasty surgical scar on her head, is a giveaway to what's coming.
Deep underground, in a maze of pathways reminiscent of those plastic mice habitats, military units are dispatched to handle a major crisis unfolding in a secret research facility. One unit comes across Eve, who doesn't remember much, but unit leader Romeo (Ditch Davey), recognizes her as his dead wife (now not so dead, of course). Between bullets and running from danger the soldiers unravel into a frenzied mess of nerves and fears--the drill for horror movie dramatics. Eve begins to remember and Romeo fears that the most. We find out why Romeo is so guilt-ridden, but that's after a fanatical scientist (what goes for mad these days) provides some explanation. Another fanatical and more dangerous scientist completes the story. Both scientists are treated to special effects scenes that are mind-blowing (for them) and gruesome for us. When Eve fully remembers, matters become much worse. The ending isn't, so there's plenty of room for a sequel.
While I agree with a few of the online critics that the movie rehashes the same hash, I disagree that this makes it a bad movie. It's cooked with enough satisfying action and pulp science fiction thematics to make it worth watching. I just wish there were more killer gorillas. Now that would have been great.