This is not a happy episode. In fact, this could be one of the most depressing hours of television in years. 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.
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.
Her death is the break between the faÃ§ade 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.
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. 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.
It's quite possible, given the cyclic nature of the story, that thousands of years ago, the Colonials of the previous cycle 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?
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. 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.
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.