  Oh, and I've been watching me some Farscape. I've watched up to episode 6 now. It's not bad- the characters are fairly interesting, the writing is ok, and the acting is ok, the effects are decent, and the puppets are cool.
But really the main difference between it and Star Trek is that it doesn't take itself as seriously. Much of it is exactly the same: all of the plots so far have pretty much been done by Star Trek already.
D'Argo may as well be a Klingon. A lot of the aliens are simply either bumpy foreheads or else they don't even bother and they look entirely human, maybe with colored contact lenses or skin tone. I do like that it doesn't take itself seriously. There are a few running gags- for example, Chrichton is constantly making referrence to pop culture and slang that confuses the others, which can be funny.
But, like I said before, it's no Firefly. It doesn't have the same kind of attitude, and while Firefly wasn't entirely original, the stuff they were borrowing from hadn't been done quite as recently as with Farscape- Firefly uses Western plots, Farscape uses Star Trek plots. And while they both have crews of outlaws, Firefly makes better use of that by actually commiting crimes rather than perpetually running. The dialogue was much better too- I can't really think of any lines I found quoteable from Farscape so far, but with Firefly there were probably five or six in the pilot episode alone.
But what they have most in common is that they were both cancelled before their time (at least, from what I've read about Farscape's cancellation). Moreso in Firefly's case- I'd have loved to have had three and a half seasons of Firefly. 
