I unfortunately (or fortunately, perhaps?) never made it to the end of BSG. I dropped it a little after the New Caprica stuff due to a variety of logistical issues making it hard to watch the show coupled with the fact that I wasn't really enjoying watching it. I thought that the first couple of years of it (including the intro miniseries) were quite nice, and I was a fan of the original BSG (which I saw in syndication as a preteen and teen).
As far as a show which I was Late To The Party on, about the only one I can think of is Star Trek: TNG. I liked the original series (from WPIX as a kid) and the movies. I remember watching Encounter At Farpoint, and then actively being disinterested in the series until about season 6. I finally read enough issues of Cinefantastique which were season reviews of it to give it a try, and then I really liked it. Never really got into DS9, however.
The only other one I can think of is Law & Order, which I never watched before I went to college and it was on 8 hours a day on A&E. Then it became a favorite for a while, especially the Michael Moriarity episodes. WHen Dick Wolf gave up day to day ops and Rene Balcer came in, the show sort of tanked, unfortunately.