Now that the introductory phase is well and truly over, complication must inevitably settle in, tossing pieces around the board in a seemingly random fashion. One problem with a deeply serialized format, particularly when a roadmap to resolution has been set, is filling in the blanks in sufficient depth. Motivations need to be established, and they must be tenable.
This episode, on the surface, is a bit boring and pretentious, and there will be a number of fans declaring it "horrible" or "filler" as a result. Some of that is a reaction to the approach, not the content. The content itself is grounded convincingly in the continuity of the series, even in instances where it doesn't seem to be the case.
Zarek has always been a dangerous figure, a political rival to Roslin with complex subversive motives. This makes him a fun character to have around, but in realistic terms, not someone that should necessarily be in the presidential role. It's not surprising that Adama would stonewall Zarek and push him out of favor, denying the Quorum any cooperation while he stands in Roslin's place. What is surprising is how well Zarek takes that opposition.
Perhaps Zarek saw where the wind was blowing, and recognized that he would have someone more pliant to his manipulations in Lee Adama. I noted in an earlier review that Zarek seemed to be grooming Lee for this role, and sure enough, now he's President Adama. His entire personality fits into the prototypical and idealistic notion of what a president should be, after all, and the writers spend a great deal of time making that case.
Oddly, they use Romo Lampkin as the messenger to the audience, and for the most part, it works. Lampkin was an interesting mentor to Lee already, so why not continue in that fashion? He's also a bit mad, so there's always a question of where the demented brilliance ends and the madness begins. The bit with the cat doesn't quite add up, but it does play well with Lampkin's style of manipulation. Forcing Lee to recognize and justify his fitness as president under gunpoint doesn't seem all that outlandish for him!
So generally speaking, while Lee continues to be a bland character (even when striking a supermodel pose in red civilian threads), his character progression fits what has come before. The same is true for Adama, though the writers seem to take his personal quest to retrieve Roslin over the line of rationality.
That Adama would risk everything, including the fleet, to find someone he loves is not in question. This is the same Adama who would not give up on Kara in "You Can't Go Home Again", and that Adama will do nearly anything. It's incredibly dangerous to have a military commander with such attachments, but under the circumstances, other options simply don't exist. Which is why, in the end, it's so interesting to think of Adama setting forth on this personal quest. He continues to risk, but he's decided not to risk everyone else in the process.
Of course, that's from his point of view; in reality, he's just placed a Cylon in control of the entire fleet (and one with an admitted history of bad command decisions). Things seem on the verge of going horribly, horribly wrong without Roslin and Adama at the helm, and yet that may be deceptive. Lee is far more likely to listen when it comes to the idea of accord with the Cylons, and this new responsibility might finally push Tigh out of his post-revelatory funk.
That said, did Adama need to resign to make this story work? I'm not sure that it was necessary, because he could have placed Tigh in charge without the additional drama. Much like the over-the-top farewell for Lee earlier in the season, it seems like the writers elected to skip the subdued approach and went for the overkill. It was particularly odd with respect to their previous argument (and fistfight) regarding Caprica Six.
Tigh's relationship with Caprica Six continues to be an odd plot point. I'm not sure that I'm sold on the idea just yet, but it's clear that this situation is meant to distinguish the known Cylons from the Final Five in a fundamental way. This must be true, because the known Cylons were unable to reproduce; that was one key component of why they had to keep some of Humanity alive. Without that factor, the Cylons could feel justified in wiping out the rest of the Colonials.
On the other hand, if my theory regarding the origins of the Final Five are correct, then Tigh's ability to impregnate Caprica Six makes sense. According to the theory, the Final Five are more software than hardware, a kind of genetic meme seeded within Humanity in each new turn of the wheel. If so, then Tigh has the right biology, since he is effective what is meant to be created. (This also means that the Final Five could, potentially, have origins older than the previous cycle.)
The main issue with this episode is not necessarily what happens, but how far the writers went to justify those choices. I personally think they oversold some of the plot turns, making them feel forced and unnatural, where a more subtle approach would have been in keeping with what has been seen. With this being the final season, and with expectations so high, maybe it's a product of a desire to make every moment count.