- A much healthier, more realistic perception of the "final frontier" - Trek came of age in the 1960s, when the possibilities seemed endless, and that there was a dire need for optimism amongst international strife. Firefly/Serenity came of age during a much similar time - only there was a greater cynicism due to events like Watergate, Iran Contra, and many others. Firefly/Serenity reassures us that although we will make it through tough times, it doesn't pretend to be utopian - more frequently, it's practical.
- The Hero of Canton, the Man They Call Jayne - When you're in a firefight, who do you want at your back: a pointy eared guy spouting obscure statistics...or a practical, soldier-of-fortune who is in it for his own reasons. (Plus, this takes the idea of a science fiction western literally - many of the crew on board the ship consists of archetypes from traditional Westerns). None of the main characters are simple - when the most spiritual man on the ship (in one episode) openly declares that "kneecapping" cannot be found in the Bible...that is a far cry from the spit-polished perfection of Trek.
- It's Not A Black and White World - Trek, at its worst, tends to divide its good guys and bad guys - usually, human = good, alien = bad. (Deep Space 9, which approached a more morally complex Federation, is the franchise entry often reviled in Trek's revisionist history). Firefly/Serenity takes place in the "Alliance", caused (presumably) by a unified American/Chinese state - although there are hints of malevolence (especially in the Serenity movie), nothing is totally what it seems. Much like Blake's 7, our crew traffics in a morally ambiguous universe - unlike B7, they clearly are criminals, often looking out for the little guy. (Hey, isn't that more of a noir quality ? If it works, so be it)
- Captain Mal Reynolds Can Kick Kirk's Butt - there, I said it out loud. Mal Reynolds probably shares more with Raymond Chandler's heroes than Louis L'Amour - he's a man who understands that the world is rough - but is not too rough himself. While Kirk would wait until his shirt was torn to fight back, Reynolds would more than likely draw and shoot. No "Greedo shot first" business - Reynolds combines a world-weariness with a sharply-drawn moral line. (Plus, I don't see Nathan Fillion whining and moaning when Serenity is rebooted in 2047).
- There's a lot less to love, but it's more lovable - The original Star Trek series has 79 episodes - add TNG, DS9, Voyager, and Enterprise, and you are well on your way to burnout. Too many hours, clunky episodes...but although Firefly/Serenity isn't perfect, the fact that there are only 13 episodes (plus the movie) makes it that much more valuable. Plus, it is of a more recent vintage, and it resonates more fully with audiences.
Although not as much as you'll love Doctor Who.