I can't agree on this point. From the beginning of season 4 they have been exploring what it means to be human by having four characters learn that they are not human. Tory abandons her humanity at the first opportunity, Tyrol slowly abandons it and Tigh steadfastly refuses to let go of the man he wants to be. You also have Cavil's rant about not wanting to be human and wanting to be a machine, which at least brought up the questions in our mind of what constitutes a human.
Saying all of that doesn't mean that there's an interesting thought in there anywhere about "what it means to be human." Actually, "what it means to be human" within the context of popular drama is a bullshit question anyway.
Why is it never enough that a story about people be observant and moving? Why do skiffy fans always indulge in this apologia about "big questions" and "teaching" and such pooh-bah? This is nothing but fodder for a C- sophomore essay.
It also explored what happens to a society which loses all hope. The mutiny, Dee's suicide, Roslin's decision to die and Adama's breakdown have all been in response to finding out that Earth is a radioactive wasteland. They asked these questions and then played them out.
This, on the other hand, is worthwhile - well, not the "society which loses all hope," which is also middlebrow bullshit in this context, but the observation of individuals
losing hope and struggling to motivate themselves has been a large part of what's driving the narrative lately and BSG makes it really, really interesting and sometimes surprising.