It is NOT about humanity fighting robots or aliens. On the surface it seems to be, but the biggest issue that they repeatedly attempt to tackle is "what defines 'humanity'"
It is by no error that the humans on the show are polytheistic while the cylons are monotheistic. In many ways the cylons look upon the pagans of the colonies as each of the monotheistic religions on earth have looked at pagans over time.
Recent episodes have also made it clear the cylons do not share one mind, and that there is dissent within the ranks. In reality, if one examines the cylons closely, one can see quite a bit of ourselves in them. So which side really is the most human? When one looks at the cylons as sentient beings with varying opinions, doesn't it raise a question as to whether the blind hatred on both sides is justified?
Looking at a cylon is like looking in a mirror and seeing the parts of ourselves that do not like to see. I believe this is why the remake placed such importance on the idea that the cylons look human.
The show has also spent significant time on terrorism, "peace" movements, child labor/slavery, the struggle between democracy and military rule, racial bigotry, and of course survival.
Where star trek is an optimistic view of the future where humanity flourishes in some kind of unrealistic socialist utopia where everyone wants to better themselves, Battlestar Galactica attempts to simulate what true human nature would do in a situation where all infrastructure were eliminated, more people were dying than being born, and the future was a dream at best. The very sobering (and realistic) result is that the strands by which civilization is held together are weaker than we think, and we take a lot for granted.
So yes, on the surface it's humans fighting alien robots and there's blood and gore sure. But there is symbolism beneath the surface, and contrary to LOAF's comments, I would argue that there are some issues addressed that are not commonly seen on other shows in the genre (or any other for that matter). It may take some deeper examination of the show beyond what's thrown in for entertainment value, but there is a treasure to be found in the depths.