Direct-to-DVD releases are tough to gague. Are we supposed to grade them using the same criteria that one would use for a theatrical release because a movie’s a movie, or should we cut it some slack because by the very fact that it’s being issued straight to DVD. even the studio knows that it’s B-grade material at best? Either way, despite the familiarity of the material and its dreadfully generic name, “Alien Raiders” is a decent little flick for fans of monster sci-fi. Carlos Bernard (Tony Almeida on “24”) leads a group of well-armed renegades into a supermarket in the middle of rural Arizona in order to stop an alien infestation, and once their “spotter” is killed, the group has to use less pleasant methods in order to determine which hostages are infected. It’s basically the plots for “The Thing,” “The Mist” and “The Negotiator” thrown into a blender, though it’s wisely but frustratingly stingy with the details on the alien species they’re battling. The acting is actually pretty decent (though a little of Rockmond Dunbar’s bluster goes a long way), but the story is rather thin, leading to the predictable “shocker” finale. Still, we’ve seen far worse movies than this at the multiplex.