Another reviewer here attributes the story on which this movie is based to "Andrew K. Dick". Well, at least he got it part right. Philip K. Dick wrote a short story called Second Variety a few decades ago, and it is on his interesting idea that this movie is based.
Philip K. Dick has been adapted before. Movies like Blade Runner [Do Androids Dream of Electric Sheep?], Total Recall [We Can Remember It For You Wholesale], and in summer 2002 The Minority Report [same title] have thrilled audiences while not remaining entirely faithful to Dick's ideas [especially Total Recall, in which Paul Verhoven took huge liberties]. Screamers holds to the idea, but not the setting, of Dick's story. To understand this story you must understand the context and what was on Dick's mind: The US and USSR [keep in mind the time of writing] have finally done it. They have finally blown each other up, and the remnants on earth fight it out in a style reminiscent of WWI. The US develops mechanized standoff weapons called Claws [the Screamers of the movie] which kill in an indiscriminate fashion. US troops are protected by wrist bands which ward off the Claws. Because the Claws are built in wholly mechanized factories, Dick takes them to another level - that of designing new weapons of their own. The obvious happens: US and Soviet armies alike are now targets. The clever, signature Philip K. Dick twist comes when the protagonist of the story finally recognizes the fact that these mechanized killing machines, just as we humans, have developed the means to start killing each other. What irony.
This movie's telling is small, yes, and it is low budget. The story does not need glitz and special effects. The story, in order to be understood, requires perspective and a recognition of what is actually being examined. Human folly is the tale here, and it is fairly well told. Enjoy this story.