The mix of comedy and drama was spot on and really ahead of its time because now the shows on tv are all like that pretty much.
Er... no. The West Wing
, to take but one example, expertly melded comedy and drama starting in '99.
More relevantly, drama-comedy had already been established as Whedon's shtick in Buffy the Vampire Slayer
. In that sense Firefly
was more of the same Whedon snark wrapped up in a space opera western format.
Firefly hits a very specific stylistic sweet spot for a pretty small number of people (see Serenity's mediocre performance),
There are very few space opera titles which have achieved really broad mainstream appeal in the nicely tangible sense of ratings and box office smashes. The Star Wars trilogy and Star Trek: The Next Generation would be two examples. Take any other space opera show popular in this subforum and you'll find a series plagued by low ratings and threats of cancellation (carried out in Farscape's case, barely avoided in Babylon 5's, Battlestar Galactica was always very underwatched, etc).
In other words Firefly really isn't very peculiar here.