The problem with the “Alien vs. Predator” series is that the humans keep getting in the way.

“Aliens vs. Predator: Requiem” is the second movie ripped off from the best-selling video game which in turn was ripped off from separate Reagan-era monster-movie franchises. That’s not necessarily a bad thing; an effective B-movie doesn’t have to be original, just well-crafted. The 2004 flick “AVP: Alien vs. Predator,” for instance, was proficient sci-fi/action snack food, nothing more or less. “Requiem,” by comparison, is a plate of nachos left too long in the microwave.

The problems with the movie are twofold and easy to spot: the acting stinks and you can’t understand what’s going on. Set in picturesque Crested Butte, Colo. (played by locations in British Columbia), the film kicks off with a Predator spaceship crash-landing on earth with a cargo of Alien lab specimens. As the critters fan out into the Colorado rainforest and begin their face-hugging, chest-cavity-incubating ways, a dreadlocked Predator blasts off from his home planet to clean up the mess.

As the town population gets thinned and the gore factor goes up, the Predator goes thingo-a-thingo with various Aliens, including what looks like a crossbreed PredAlien. Where he (she? it?) came from isn’t very clear, although it may have something to do with a mysterious syringe that gets injected into somebody at some point. The Predator also carries a vial of glowing blue liquid that dissolves whatever it touches. I found myself craving a bottle of the stuff and devoutly wishing it were retroactive.