The previous episode ended with the Colonials and renegade Cylons standing amidst the ruins of a world called Earth, just moments after the remnants of Humanity celebrated their potential deliverance. The better part of this episode is devoted to the psychological fallout of that crushing blow, and the results are stunning, to say the least.
This is not a happy episode. In fact, this could be one of the most depressing hours of television in years. Not one person is happy, not one person is remotely satisfied, and not one person is left unscathed. What makes this such a powerful and perfect episode is that the audience can understand the characters' reactions. In a sense, we're all reeling from the realization that Earth is not what it was supposed to be, and that there is no obvious direction for the future. Worse, they all know that Father Cavil's faction of the Cylons will be showing up sooner or later, and there will be no magical resolution to that problem.
Dee's suicide is shocking in the moment it happens, but after re-watching the episode, the writers did a very good job of leading up to it. Dee's loss of hope is palpable from the very beginning, and her "date" with Lee seems as much about saying goodbye as it is about pushing Lee in the right direction before checking out. If it doesn't seem to quite make sense, I think that's intentional; Dee is not in her right mind, so it's hard to grasp her rationale in detail. It's simply obvious that the discovery of a formerly Cylon-populated, ruined husk of Earth annihilated her mental stability.
Dee is essentially our window into the psychological torture experienced by the entire Colonial fleet. Her death is the break between the façade of civility and the unbearable truth. Adama completes the picture; those who look at Dee's decision and wonder if that's what they should do as well. Frankly, I'm shocked that there weren't more suicides. If Adama had pushed Tigh into killing him, I imagine it would have all been over.
As it is, there's now a massive power vacuum. Roslin has all but checked out and the primary religion is under serious question. Lee could make a case that he should stand in Roslin's place, but I expect Zarek to make a move sooner or later. After all, he was the one who pushed Lee into the limelight in the first place; he has definite ambitions. I also expect Baltar's new religion to become a lot more prominent in the days to come, as the Colonials cast about for something to believe in.
Amidst the crushing despair, there were amazing revelations. Nearly everyone is taking Earth for granted, but it may not be what it seems. Baltar and the others conclude that the thirteenth tribe consisted of Cylons, both Centurions and "skinjobs", and that they arrived on this particular world and called it "Earth". Does that mean that it is, in fact, Earth?
It's quite possible, given the cyclic nature of the story, that thousands of years ago, they were also searching for Earth, hunted down by their own Cylons. Who's to say they didn't end up finding a burned-out Earth themselves? They could have simply found a new world, called that Earth in memory of the "original". And then, like now, they could have gone about the business of merging Humans and Cylons into a race of beings like Hera and Nicholas.
After all, the bones were Cylon, but why does that necessarily mean that they were Cylons as we know them? They, too, appear to have lost the ability to resurrect, or the survival of the Final Five wouldn't have been so extraordinary. And because Tigh and the others were known since they were younger, and they aged like normal human beings, it stands to reason that their own resurrection was not in the usual Cylon style.
This harkens back to one of my original theories, one I've mentioned several times: that the Final Five are Human/Cylon hybrids from the previous cycle who managed to persist until the next cycle. How that happened is still to be determined, but it must have involved some kind of regenerative program. Perhaps it was something that the Five sent into space before the end came. One might suspect that the nuclear destruction of Earth came from the previous cycle's analogue to Father Cavil and his Cylon faction.
Something tells me that the restoration of the Final Five is directly connected to Kara's restoration. Kara was dead, her Viper destroyed. That being the case, how was she reborn? Everyone assumes that Earth is completely dead, but someone (or something) had to resurrect Kara and her Viper. Perhaps something that didn't see or know the difference between man and machine? Something that was programmed or designed to recreate members of a Human/Cylon hybrid species?
If so, the whole question of the fifth Cylon's identity becomes moot. That individual is no longer a factor; how they came to be in this time is a lot more important. Kara's very existence is more important than Ellen Tigh's true nature. Piecing together the puzzle of what the Final Five really are, how they survived, and how and when they came to intersect with the current Cylon population is the major mystery to be resolved.
Not that the question of the final Cylon wasn't front and center. This is another aspect of Dee's suicide; they were clearly using Dee as a red herring for the revelation of the fifth. The same applies to Kara (though, admittedly, I believe she's connected to the Final Five in some way). Just the fact that the writers were able to keep the central mysteries front and center, while dealing with the despair of the fleet was such depth, is a testimony to the excellence of the episode.
From the script to the performances to the direction to the score, everything came together to make this one of the best episodes of the series in a very long time. This is easily the best episode of the season, even topping the powerful "Revelations". What makes this truly astounding is the realization that there are nine more episodes to go until the end.