I never even knew about it when it was on. A guy from work, uh, "arranged for me to get a copy" of the first three episodes, and I really enjoyed it. I thought the soundtrack was excellent. I'm now waiting for him to make the "arrangements" to get the rest of the series...as soon as he's done "reviewing" my complete "Get Smart" series.
Not to sound all righteous or anything, but it really IS worth the $40 to buy the box set. You won't be disappointed, if you've liked what you've seen so far. Support your favorite production staff (writers/actors/directors), or they won't be working anymore, and all that. I'll pay for NEARLY anything Joss Whedon had a significant hand in, 'cause he's just that good.
Pick up a copy of 'Serenity' as well, if you haven't yet. My fiancee saw that first (when she was still my girlfriend) with me, loved it, and went back and watched my 'Firefly' DVDs. She said she liked 'Serenity' a little better, but still liked 'Firefly' a lot.