For those of you that don't watch, all you need to know is that the basic premise is as follows. Human beings created the Cylons, mechanical robot-types, to aid in the colonization of new planets. These human-made creatures then (with no explanation yet forthcoming by the way) "rebelled" against humanity and thus began the first human-Cylon war. The humans apparently "won" this war, or at least, the Cylons bugged off and left humanity alone for 40 years, during which time human civilization on the Twelve Colonies started to revert back to its techo-dependent ways. As the first episode (the mini-series) opens, the Battlestar Galactica is a military relic about to be decomissioned, and the Commander of the Battlestar (Commander Adama) is himself a relic with old-fashioned fears of the consequences of networking computers. But, of course, his old-fashioned paranoia is vindicated when the Cylons reappear without warning and nuke all twelve Colonial planets, as well as the entire military fleet, save for the obsolete Galactica. Adama then becomes the de facto leader of the remnants of humanity--those survivors who were in transit off-planet during the nuclear attacks that killed everyone else.
So that's the premise. What is terribly interesting is that as the story develops, there is constant commentary on human nature. During a grand tale of somewhat epic proportion about the gutsiness of humanity, its determination, will to survive, capacity for sacrifice and courage, and inexplicable optimism in the face of overwhelming odds, there is also a consistent message that humanity is inherently flawed: shortsighted and violent, selfish and ruthless. There is even the sense that this doomed fate, as the result of ignorance and a failure of moral responsibility, is deserved even as they try valiantly to escape it.
Quite often this commentary on human nature is directly voiced in the dialogue. At the end of the original miniseries, a group of Cylons convenes to discuss the escape of the Galactica and the fleet of civilian refugee ships it protects. The humans have temporarily placed themselves beyond the Cylons' reach, and the question is, can the Cylons afford to let them go? The answer is a decisive "no," and the reason is very simple. If the Cylons are merciful and allow the humans to escape, they predict that the humans will return to exact revenge, because "it is their nature." The irony, of course, is that this is exactly what the Cylons themselves have done: but this goes unremarked, and apparently unnoticed by the Cylons themselves.
Also intriguing is that one of the major Cylon characters, "Number Six," refers to the Cylons as "the children of humanity" in a conversation with another Cylon. They discuss the concept of a debt owed to their parentage and the conclude that parents must be supplanted by their children, in fact, die, so that the children can "come into their own." But the condemnation often voiced by Cylon characters of the inherent depravity in human nature is never considered by them as a possible heritage from their human "parents."
Intensifying this commentary is the religious contrast quite deliberately drawn between the (ostensibly) polytheistic/atheistic humans and the strictly religious monotheistic Cylons. Not only are the Cylons physically and technologically superior to humanity; they consider themselves religiously superior as well. The sense of self-righteousness that runs blatantly through all Cylon God-talk serves to further obscure the obvious question of the parallel depravity of Cylon-nature as the Cylons consistently condemn human nature.
There's much more to this series--a lot of other questions and issues of a posthuman nature are raised. But this particular theme runs quite strongly throughout the whole series, and is central to the plot. The unanswered question of why the Cylons rebelled in the first place has a shadowy hint of an answer in their constant condemnation of human nature. The desperate decisions forced on Commander Adama and the fleet--who do we save? who do we abandon? when do we give up?--illustrate the kind of ethical quandary that best exhibits the ambivalence of human nature. Whether the Cylons are correct in their assessment of human nature or not remains an open question, and I think, perhaps the determining question concerning the direction of the continuing story.