As you know from my praise of Dr. Horrible's Sing-Along Blog, I'm a fan of Joss Whedon. He's an inspiration to me personally as an aspiring television writer as he blends art and entertainment. Though I haven't watched a lot of Buffy, I'm going to go out on a limb and say Firefly is the best representation of Whedon's work.
The plot centers around a ramshackle old spaceship, populated by "the kind of people the Enterprise would just pass by". Think of it this way: science fiction is cool; westerns are cool; ergo, a well-done science fiction western must be AT LEAST double-cool, and I think you'll find it's quite a bit more.
Sidebar: WHHHYYYYY, WAAAAASH? WHYYYYY!
Anyway, it had a really short run, but it was followed up by a movie that ties up a lot of the loose ends, and there are comics and supplementary materials galore. It's a lot higher quality than most TV shows, and a whole lot more entertaining. You can watch it for free on Hulu. Check it out.