While I haven't quite finished all of the episodes yet (I'm loving them so much that I'm trying to make them last as long as possible), I can safely say that I Firefly has equalled Farscape in my affections. They are very different kinds of shows, but both have excellent dialogue and plots, unusual scenarios and above all, characters that you deeply care about.
I got the feeling when I watched Serenity that knowing about the back-story of the characters would have considerably deepened the film, and I now know for sure that that's true. The events of that film (and I really don't want to provide any spoilers here) would be that much more emotionally involving having got to know the crew properly.
Since Firefly is so character-driven, I thought that I'd give my impressions of each of the main characters. They already feel like old friends.
Captain Malcolm Reynolds
Mal is a born leader. He has the kind of quiet authority (usually asserted without throwing his weight around) that makes people follow him. It helps that he's essentially rather a good man; he's tough, and he might technically be a criminal, but he has a strong code of ethics that he sticks to, sometimes to his own disadvantage. The crew know that he will look after them, but he's not afraid to make unpopular decisions for the good of the ship and the whole crew (ordering Wash to leave the seriously injured Zoe to sort out navigation comes to mind as an example). He's as stubborn as a mule, and doesn't like his pride to be wounded, but he can also be amusingly self-deprecating at times. He secretly loves Inara (and she him), but they are both too stubborn and full of pride (and perhaps too frightened) to admit it.
SAFFRON: In the maiden's home, I heard talk of men who weren't pleased with their brides, who...
MAL: Well I ain't them. And don't you ever stand for that sort of thing. Someone tries to kill you, you try to kill 'em right back. Wife or no, you're no one's property to be tossed aside. You got the right same as anyone to live and to try to kill people. I mean, you know. People that are... That's a dumb planet.
I felt that Zoe was one of the characters who didn't come across very strongly in the film, but having seen her in Firefly, she's one of my favourite characters. Zoe fought in the Unification War with Mal, and so shares a kind of quiet, respectful comradeship with him. Despite the occasional bout of jealous paranoia on the part of her husband, Wash, there doesn't seem to be anything going on romantically between her and Mal; they trust one another implicitly, and their long association means that they generally understand one another without saying much.
Zoe is a quiet, tough, efficient fighter. You get the feeling that she doesn't particularly enjoy violence, but she sees it as a job that someone's got to do, and one that she happens to be quite good at. She and Wash have a very interesting marriage (something I'll come on to later). While she technically outranks him, they have a tendency to address one another as 'honey' on the ship, which is very sweet. Zoe has a bone-dry sense of humour, with some wonderful deadpan lines that you might miss if you're not paying attention. There's a wonderful scene in 'Our Mrs. Reynolds' which, for me, encapsulates Zoe's humour and her relationship with Wash. Saffron (Mal's accidentally acquired wife) is being exaggeratedly wifely, making Mal dinner, and offering to wash his feet. Wash makes a comment about it in a way that could be construed as approval, then catches Zoe giving him The Look. He looks at her as if she's a grenade with the pin pulled out, then adds hurriedly:
ZOE: Remember that sex we were planning to have ever again?
Wash (the pilot) is like a big, floppy golden-haired puppy. He always wants to be at the centre of the fun, included in the jokes, but can also get lost in his own whimsical world. He even plays with toy dinosaurs at the helm when he gets bored:
WASH: This is a Fertile land and we will thrive...
WASH (as stegosaurus): We will rule over all this land, and we will call it... This Land.
WASH (as T-Rex): I think we should call it... your grave!
WASH (as stegosaurus): Curse your sudden but inevitable betrayal!
WASH (as T-Rex): Ha HA! Mine is an evil laugh! Now die!
Needless to say, he loves Zoe to bits, and seems to be constantly astounded at his luck in ending up with her. What he probably doesn't quite realise is that Zoe feels equally blessed to be on the business end of his unconditional love. He isn't especially brave, but he is clever, and sweet, and one of the funniest people on board. The word 'uxorious' could have been coined with Wash in mind.
Between those three characters alone, we have one of the best depictions I've ever seen on film of both the bond between two people who have to trust one another with their lives, and between husband and wife.
[Quotes courtesy of the Firefly Wiki]
In Firefly - Part Two, Jayne, Kaylee, Simon, River, Book and Inara.