Let's put it this way: our standards have been set by Star Trek TNG, DS9, Doctor Who, BSG, and now Firefly. We're looking for a show that good.
If you want more SF shows on the same level as those, I'd suggest Babylon 5 and Farscape.
Farscape? Really? I've heard literally nothing about it. You would say it's that good? (That's the one with the Henson workshop, right?)
I saw the first 3 seasons or so of Babylon 5 many, many years ago, and thought it paled in comparison to Deep Space Nine. The people playing the four ambassadors were all fantastic, but the actors playing the actual crew (especially that second-in-command) were mostly quite mediocre, I thought.
Anyway, maybe I should be asking people about Farscape too....