So much new in the last few episodes of BSG

Well, the fifth Cylon remains a mystery and three of the four almost went out an airlock, but they have now been revealed. This is interesting since they have had no desire to kill the humans. Why were they suddenly activated with that Stones tune? Was it just to get all of them to earth and if so, who activated them? And now, just look at earth. A barren rock. The hint seems to be that we all killed ourselves off and now the humans and the cylons have nothing to live for any more. Darn shame. If this is the mid-season finale, as Scott Ian's blog calls it, then where do they go from here? Lots of questions and not many answers.