Said it already (link) but it deserves to be said again -- this was the best serial-drama I've seen. While some questions were left unanswered in the series finale, in all, the drama was a beautiful human play of philosophy, ego, spirituality, religion, science, politics, revolution, life, and death.
This is one of the few serial-dramas that people will watch over and over again, and think something new each time. Ron Moore (link) did an excellent job -- for an American television show.*(read more on this point, after the continued -- but be warned, it may be a spoiler)
Overall, I think newcomers will wonder how in the hell they didn't know about it sooner (it was too complex of a story for broadcast television -- and would have been deemed too complex for basic pay-TV if it weren't for the creative battles that the writers fought and won against NBC Universal). The good thing is that it's never too late to give it a try :)
[Battlestar Galactica: Season 01 Episode 00 (Pilot)]
*That said, it is still an American television show, which always comes with all of the fantasy of white American minds. From a non white American perspective, the entire show could be easily dismissed for suggesting that "alien" white humans are responsible for our civilization as opposed to an original human who evolved organically out of Africa.