I'm actually working on a Serenity/Firefly "inspired" setting ... my group wants to eventually play something sci-fi and I wanted something a little more country, so I suggested it.
I HATE mucking about in other people's IP, though. The good stories are usually taken and then there's the whole "Howzit supposed to work?!" issue.
Personally, "it just couldn't be like that". I.E. either the technology exists to terraform even wildly inappropriate stellar bodies and make them utterly Earthlike ... where-upon the whole wild-west "Ain't got nunthat fancy Tech No Lo Gee here, ayup." doesn't fly. (You don't spend seventy-bazillion dollars to add gravity and an atmo to a moon then toss people with sheep and some hatchets on there. And if tech is so advanced it's cheap to do, then there's no REASON people should be so tech poor. Building hatchets would probably be MORE expensive than graviton lasers and insta-housing.)
Or you've got quick and easy FTL. But nothing really suggests FTL in Serenity.
What closes it for me is all the times in the show where they've been "traveling" from one place to the next and something goes wrong. Our Mrs. Reynolds, when there's the net and they're traveling slow enough for Jayne to shoot. Mmm. The ep with the bounty hunter. The ep where the engine breaks and they have to abandon ship. All of these "between the planets" things take place at what appear to be "normal" speeds.
But it doesn't MATTER ... it was a good show.
But if I'm going to play a game in it, some different things have to be known. For a TV show, how long it takes to get from A to B can be set once, because that's the only time it'll ever come up. And stuff can just "happen" because it's good TV. But in a game, the players want to know all the distances between places, and they don't want their ship to "throw a space rod" and get boarded by pirates for no reason other than I thought lack of oxygen and a firefight would be cool this week.
In a TV show, guns go bang. The main characters never get hit until the plotline says they get hit, and then they survive based on whether or not the actor was dumb enough to ask for a raise too close to the season finale. In a game, the characters get shot at and should face danger every fight, and they should survive based on the skill and luck of themselves and the guy with the medkit. Players want to know what "stats" each gun has, not just what looks the coolest on the screen. And, usually, what looks cool doesn't apply to the PCs as much as what kills the other guy. (I.E. are the PCs really going to walk around with revolvers and sawed-off six-shot rifles when there are obviously automatic rifles and autoloaders available? They're even available to "civilians", based on the Wall-o-Guns that Jayne has, including Vera the assault rifle and a few autoloader pistols. So why does everybody else walk around all Old West?)
And, biggest ... when have you EVER known Player Characters to ride around in a spaceship without any guns? It may be more realistic, but my players would throw a fit. Especially with "monsters" out there in space. I can hear it now: "There are RULES for guns on ships, though, right? Right? So ... how much to put a hidden gun on the ship?" And from there it's a quest to strap a flak gun on the ship. (ooo ... darn, beat me to it).
It's a great show ... I don't think it would be that great a game.
--fje