Oh, if you liked Buffy, you'd probably like Firefly, too. It couldn't decide whether it was a western or a space opera, and in fact, it was the only western I ever liked. It has Joss's usual spot-on casting and his talents for understatement and witty dialog. The special effects were great, too. Like all of Joss's work that I've ever seen, there's the expected frail-looking mega-deadly cute girl. Joss also isn't afraid of killing off a star if it's right for the plot. It also lives on the gray line between moral right and wrong, much like Buffy did. Great stuff.
Sample dialog: "Well, my days of not taking you seriously are certainly reaching a middle."
Oh, big guns, too. I even named one of my registered .50's after a gun in the show: Vera.