Add me to the "absolutely never ever watch Firefly" camp. I've seen the entire series and the movie, so I am speaking from experience.
I'm also a huge Buffy/Angel/Avengers fan, so it's not like I'm a Whedon hater. I'm also partial to a number of actors on the show, as they've been in some of my favorite series at other times (Baccarin, Staite specifically, but of course the entire cast was on Buffy/Angel at some point).
It's just a terrible, terrible, terrible show. (That's a grand exaggeration, by the way. It's not all that terrible. It's just that the only way to combat the extreme fanboi love of most Firefly fans is to really go to the other end of the spectrum.)
If you are a huge fan of a show bashing you in the face with the horrendous gimmick of using Mandarin Chinese to replace swear words (it's worse than the "frack" thing in Battlestar), then by all means, watch the show.
But really, don't ever watch it.