I confess to being somewhat worried that BSG has placed so much store on the reveal of the final Cylon. To my mind, the most crucial questions of the series--by which I mean, the questions that, if answered in a satisfying way, would make the series a final success--were:
(1) Where do the humans go?
(2) What was the original Cylon plan?
(3) Is there a reconciling between human and Cylon cultures?
(4) Whose theistic views are correct? The pagan humans or the monotheistic Cylons?
I've always thought that if Ron Moore et al could answer those questions is a satisfying way, then the series would have an enormously successful conclusion. Instead, we seem to have reached a place where series turns on a twist reveal, like an M. Knight Shyamalamalaman movie. Narratively speaking, I think that's dangerous ground on which to make your final stand.
All of that said, I'm not as down in the mouth as Gregg Easterbrook, who says that nothing about the Cylons makes any sense.
Instead, I'd posit that everything about the Cylons makes sense, if and only if the Cylons are right about there being one god. If the Cylons are right, then we can view the series as grounded in a sort of Old Testament ethos--a universe where there are prophets and visions and the hand of god actively moves among the earthly. If that's what's going on, then we can explain and believe the Starbuck's visions, Leoben's prophecies, etc.
Also, if I were a betting man, my guess would be that Adama is the final Cylon. He's the only character who makes sense narratively, logically, and theistically.
5 hours ago