The great thing about Firefly is that it takes itself a lot less seriously than the other Joss Whedon series did. I think this is mainly a result of casting choices (Sarah Michelle Gellar can't do comedy to save her life), but is also certainly the result of better writing. Several characters definitely have the Bruce Campbell-esque type of outrageous yet exceedingly cool lines that show that although the series is definitely serious at times, there are other times when the only people who aren't laughing are those without any sense of humor at all.
I really hope Serenity maintains that balance between tongue-in-cheek and drama, because it would be too easy to just focus on the drama when you put it on the big screen. The previews seem like they're keeping the same dose of snark that made the show awesome, so I am pretty psyched about the movie.
