Firefly is by the director that did the Buffy the Vampire Slayer series on TV. If you like the witty writing from that series, you'll like the way the characters interact in this one. Lots of good one-liners. Great character development over the course of the series.
I like the Firefly universe... it's a huge melting pot of cowboy/frontier stuff with a bunch of other cultures or time periods mixed in depending on the planet they are visiting. Huge asian influence, presumably becuase of the sheer numbers of Chinese that ultimately made it out into the galaxy. The characters swear in chinese, and have their own slang too. Most of the planets they visit are "frontier" planets that are old western, but there are also some that are very technologically advanced (like blade runner type planets), and others that have a Victorian way of life (with technology hidden behind the scenes). This mix of the old and new makes it interesting and fun.
I've watched Firefly since it was on TV the first time, but I've had a lot of friends who haven't come up to me and tell me how much they liked the Serenity movie. I'll point them this way to get caught up!