One of the things I really liked about the show was the fact that these people may not have been "sanctioned," but they definitely carried the banner of heroes, whether they intended to or not. Even though the main goal was to "find work & keep flying," oftentimes that work meant doing the right thing even if it was a crime against the Alliance to do so, and when presented with the moral choice, Mal always did the right thing, and expected the same of his crew. In that way, he was as much the "Star Trek
ideal" as one could want.
The characters were much more diverse than Trek
ever offered (even with Maquis on board, how 'diverse' was the crew of VOY, really?), and even if they spoke with very unique dialects and cadences (esp. Mal), I always thought their dialogue was a lot more natural than most other SF TV or movies; I also never really felt that there was anything sarcastic or too self-aware about any of the dialogue, but maybe it's that I think, and often speak, much the same way (just not sprinkled liberally with Mandarin
FF wasn't so much sci-fi as it was future fiction - these people were normal folks who just happened to live in the future, where all the tech was just part of the landscape (like cars are now) and they were going about their business, not trying to explore the limits of science. Like any genre, it's as much how the story is told as what the story itself is about, and FF was real storytelling; if you like that, you'll probably like Firefly