Just to be a vocal counterpoint, I hated Firefly, and probably for the same reason I hated Babylon 5 and the current Battlestar Galactica (not the original), and Voyager, and soap operas in general. (And probably Buffy, although I never started watching Buffy.)
The story arcs are too long.
I want my excitement to climax in 50 pages, and then conclude. Even two parters frustrate me.
I find it odd that I'm on the opposite side of the fence from the "MTV-Generation". They like the long story arcs, but they want videos cut every four seconds and shaky-cam handheld shots. I want good one-hour dramas, and nice decent photography.