But does it really?
Maybe it helps if I put it this way. I kinda get the mindset behind this. With the exceptions of Inara and River, the crew of Serenity is made up of "Bad Guys" and outcasts trying to make their way in a society made up mostly of people that would be morally opposed to who they are and the things they do to survive, which are rarely legal and even more rarely moral.
That's not what I see at all. I see a show about a group of people who have found themselves on the short end of the law through sheer overwhelming circumstance rather than choice.
Jayne is the only one of the lot who could be called a "bad guy"; really; we like him 'cause he's funny. (I heard in one revision of the concept his character was supposed to be killed off fairly fast, but Adam Baldwin's performance changed their minds.) Mal keeps him in check, mostly.
Speaking of Mal, he has no compunctions about doing what's necessary to protect his crew but will always do the right thing given the option. He's an intriguing combination of ruthless and compassionate, and believable as such despite the apparent contradiction.
Zoe, similar though driven more by loyalty to Mal than principal. I feel she could turn pretty dark without the stabilizing framework Mal and Wash provide her, though. Wash for his part probably wouldn't have stuck with the crew as long as he did if not for Zoe; he's too chipper for the rest of them, really, and truth be told he doesn't seem to like Mal overmuch.
Simon's all about protecting River, and as we saw in flashbacks, he tried quite a few things to help her before turning to force as a means of getting her out.
Kaylee, whom no one can't love. All smiles and sunshine and strawberries. Enough said there.
Book, the enigma. He's clearly a good man, but you get the definite sense that he may not always have been. What happened to change him? His story may never be told in full (until that rumored comic comes out?), though.
You mentioned River and Inara; one a victim of the State, the other keeping a secret but outwardly the most respectable of the lot.
Outcasts, certainly; being on the losing side of a war can do that. Bad guys, certainly not. They break the law when necessary to keep food on the table and gas in the engine, and even kill when they're forced to, but they're basically good people, morally speaking.
The same except nobody wears clothes or uses weapons that look like they were made in 1876
Stylistic choice. Advanced sonic and laser weapons were clearly used by the Alliance military, and Mal even had a mean-looking assault rifle in one of the war scenes, but the high-tech stuff is strictly controlled (often illegal for private owners), and the infrastructure of the border planets is such that it would be difficult to keep one maintained as easily as a simple pistol. Said pistol doesn't *have* to look like a six-shooter, but I understand why they'd make that choice in the art department. Still, the sound effects and apparent magazine size suggest at least somewhat advanced workings.
Additionally the "old west" design complements another stylistic choice of the show----that the future is made up of scrambled-together aspects of the past. The "old southern" high culture on Persephone, for instance, or the Chinese origins of the Companion's Guild.
and given that it's set in the Asian Pacific it doesn't involve cattle rustlers or ropin' and ridin'
I don't think they ever took the metaphor *that* far. The crew is only shown riding horses when it's the only practical transportation available and speed is required (I only recall two instances, actually). There was no roping that I recall, and the only cattle-transport job they did was one of the less illegal ventures they engaged in, and no rustling was involved.
and nobody's speaking an Asian language that you wouldn't expect to be speaking it.
Why wouldn't you expect them to be speaking it? Is it hard to believe that America and China would be the two nations with the greatest spaceflight capability if an Exodus from Earth were required in the next hundred years? Or that, with a few hundreds of thousands of survivors at most populating a whole new solar system after perhaps decades on generation ships, the two cultures would become inextricably entwined?
The content and trappings fit in the overall context.
They do in Firefly as well; it merely requires some deeper exploration of the premise to fully understand it. That very non-obviousness is part of the appeal.
I want to thank you for making me think through all this again, by the way. It's given me a few ideas for my Firefly mod of
Escape Velocity: Nova.
It's hard for me to come up with a definitive "Top 10 BEST", since I haven't seen all of the shows mentioned so far and criteria vary so greatly. BUT I will give it a shot. 
Lost comes closest.
