Spoilers. But that's obvious.
The best thing about the finale is that they tied up the plot completely. I don't like it at all when writers try to play it cool by leaving entire parts of their plotlines unfinished at the end, for the sake of “unanswered questions.” That's not how that works. Plotlines should always be finished, and in this regard BSG did very well.
The worst thing about the finale is that they got Starbuck's ending all wrong. In the context of her character arc, it didn't make a lot of sense. Dubious direction storywise, terrible execution dramatically. For what we ended up getting out of her, I think Ron Moore's focus was much too Starbuck-heavy these four years.
Baltar's ending was the best of all the characters'. It was an excellent conclusion to everything his character had been though.
However: It is either a credit to Moore's courage or (more likely) a sign of his negligence that Baltar and Caprica Six, the two people most directly responsible for destroying civilization (human and cylon alike) end up getting to live in paradise together on Earth. I never forgot how Six casually broke the baby's neck in the miniseries, and I never forgot how unconcerned she seemed throughout the run of the series about what she had done (not to the baby but to humanity). She was clearly repainted as a sympathetic character in the third and fourth seasons, but I never could sympathize with her. To a lesser extent, Baltar also got off too easily. He was slime; he finally did redeem himself in the end, but I found it hard to accept that people could be so blasé about his past wrongdoings. It's not that I don't accept that people can't be rehabilitated, or that they shouldn't be able to have a fresh start. I simply think these two never did the legwork to earn it. I know that life isn't fair, so I'm not complaining that they got away with their wrongs...just that it seems unrealistic.
Adama's ending was goofy. It makes no sense that he would permanently leave his son behind. Everyone else was okay. I'm glad they didn't kill off Helo; when it looked like he was done for, I was thinking that not only would it be such a cliché, but also that killing off him or Athena would have meant that the series had ended with not a single intact family remaining.
Given that half the episode was a denouement, I also would have liked to see what became of the few remaining bit characters that hadn't been killed off. Moore made a big mistake by killing off most of the supporting cast this season, and he blew it again by leaving the rest of them hanging with this finale.
I have two other big gripes about the ending: First of all, it is completely unrealistic that everyone in the fleet would have agreed to go native. I could write a great deal more about that, but that's the bottom line. It was totally illegitimate for Apolla to have to convince no one other than his dad.
Second of all, the finale was way too preachy, especially when Moore pushed his civilization-is-evil theme harder than usual in the last half-hour or so.
One mostly positive aspect of the ending, in stark contrast to the series as a whole, was its focus on interpersonal relationships. BSG always seemed uninterested in interpersonal relationships. The few that were present never got the development they needed. Writers these days seem lost when it comes to telling stories that don't have an urgent external conflict driving them forward. We'd have cared about these characters more if there had been less soap-opera melodrama and more characterization. At least the finale gave some attention to those dynamics.
A side gripe: The “maleness” of BSG's point of view was always hanging in the air, spoiling the view. There were not many females in the main and supporting casts, and most of them were killed by the end of the series. Among those female characters who were important to the story, their importance was primarily in terms of their relationships with males. Worst of all, BSG's paucity of interpersonal relationships hit females disproportionately hard: In the entire four years, there was only one instance of a strong female relationship (Kendra Shaw and Admiral Cain in the sideshow “Razor”). There's something called the “Bechdel test,” named after the person who created it back in the '80s, which serves as a rough measure of the male-centricity of a story. The “test” is that there must be more than two female characters, who talk to each other, about something other than a male. That sounds like it should be a low hurdle, but BSG still failed—and failed hard. The result is that, by the finale, the story felt heavily imbalanced: male writers telling a male story about male characters. BSG was a step forward in creating a setting where females and males were equal, but the creators themselves still had to labor under their own biases, and it spilled into their show. I'm not surprised that they never found that elusive female audience.
I was right about Earth. I noticed during the “Earth” episodes that they never showed a picture of the planet's continental geography. I knew that couldn't be a coincidence, because the shape of the continents is the one—and only—piece of “definitive” proof in a story like that one as to the authenticity of Earth. I hadn't anticipated, however, that BSG took place in our distant past—even though that deduction was more obvious.
I was right about Galactica itself: Moore had always taken care to show the accumulation of damage to Galactica's hull as the series carried on. When those first splits in the hull showed up, I realized that the “dying leader” was the Galactica itself and not President Roslin, and that the Galactica would be destroyed or scuttled once they found Earth. (Alternatively, I was prepared for a cynical ending as well, where humanity was destroyed except possibly for one or two people.)
The drama of the finale was pretty good in spots. For example, the images of Adama and Tigh on the phone with the ship under attack were very effective at conveying the action. The resolution of the opera house mystery, and Baltar's Big Moment thereafter, was also compelling. And the idea that Six and Baltar's entire purpose had been to keep the kid from taking a bullet after four years seems delicious. However, generally speaking, the finale's drama was lukewarm. Here's the worst of it: For Galactica to have won that battle was frankly impossible. Once again, the heroes triumph against overwhelming odds and save the day! Hah. I am very Not Impressed with yet another appearance of that miserable cliché.
All in all, given what we've gotten from BSG over its four seasons, the finale was very good in relative terms, and okay in absolute ones. Considering how much I paid to watch it ($0.00), I'm going to stick my thumb up in the air and smile.