Pre-Amble: I am not a Sci-Fi fan. I like some Sci-Fi short stories, but I generally consider them a guilty pleasure on par with Coheed and Cambria. I consider the whole genre largely juvenile even at it's best (I know, I know. I can't help it, I've read the classics, even.)
I know I'm LTTP, but I've been DEVOURING Battlestar Galactica for the last 6 weeks. I'm about halfway through Season 3 now.
The real power of Sci-Fi, for me, is allegory. Allegory allows you take a familiar situation and re contextualize it. There is boatloads of allegory in BSG- From the debate over theories of governance at the end of the first season (Ala Patriot Act), to the Human insurgence at the start of Season 3, there's just a ton of real world allegory that gives you a grounding in a world of interstellar space travel and killer robots.
But it's the other two key components that really sell the whole package- The unpretentious, subtle philosophy working in the background (What is it that entitles us to person-hood?) and the genuinely very real characters. They don't always act like they should and sometimes they get bent to fit the situation at hand (i.e. When Adama tells Lee that Kara got married. Adama is usually totally on point- Lee looks like he got sucker punched, but Adama is all "WHATEVS". I know he's still high from smoking up with Laura, but still), but there's such a genuine chemistry and sense of consanguinity between these characters that every bend in the road hits like it's real. And, again, allegory drives that home.
There are some clunker episodes (The start of Season 2 was awful. We got a B-grade Vietnam war movie, a slasher film and some leftover pieces of a Star Trek: Next Gen script.), but I don't think there's been an episode yet where I didn't go, "That's one of the best things I've ever seen on television". I consider myself a bit of a TV connoisseur- I know my Newsradio from my Six Feet Under, my State from my Mr. Show, the Wire from Mad Men, Dead Like Me from - and there's nothing that has such a complete punch. A lot of those shows are more refined in one way or another, but none of them feel as big or as important as BSG.
I just finished watching "Unfinished Business" and it was. That scene where Lee and Kara are out in the desert on New Caprica has all the staging of a cheesy rom-com, but it feel so real and so genuine that it just hurts. It's the mix of anguish and hope and despair and happiness that makes the whole thing sing. So many shows do one of those well (Mad Man has existential anguish down PAT. The Sopranos introduced us to the glories of gloomy moral ambiguity), none of them blend them in such an organic way. And let's discuss Katee Sackhoff for just a moment- Her little girlish squeak after her pronouncement of love just sells the whole thing, it is absolutely one of my favorite moments in the history of performances, period.
I'm gushing and I could go for days. But if you're on the fence about this like I was for years, just jump in. I can't imagine it not thrilling you.