Firefly was an awesome series. I have the DVD set, but am thinking of getting the Blu-Ray set, and giving my DVD's to my roomie. And yes, it's visuals were extremely good....too big for the small screen....and sadly, that's what killed the visual impact of Serenity on the big screen for me. It just didn't have that leap of quality, visually, like Star Trek The Motion Picture did.
That said, Serenity is a good story, but unfortunately, was done a bit niche. As openly accessible as it tried to be for newcomers, it was really a movie for the fans, The Browncoats.