If detective series had been as poorly represented as scifi through the years, Scooby Doo might be a good example of a detective series.
Campy, cliched, unimaginitive - and that's the good ones. :-) Star Trek TNG was good for its day but has aged very badly, and later spinoffs were very poor, with feeble characterisation and weak plots, usually involving some kind of time travel. By the end they just stopped relying on stories to attract viewers and just got buxom birds in tight catsuits to do that. Some unwritten Star Trek law goes that, the more episodes you make, the crapper the theme tune and the duller the characters have to be. And the tighter the catsuit.
I suppose Babylon 5 managed to prop up the scene for a while in the mid 90s, but latex aliens and its degeneration into a war of Light vs. Shadow threw it into the Bad Scifi Cliche Bargain Bin (which Farscape, Crusade, Andromeda and their ilk have never actually crawled out of since the beginning).
Lexx was startlingly original (not to mention pervy), but it eventually got really, REALLY boring too, taking whole series to tell a story that could be done in half an episode. This fate had been suffered the last series of Dr. Who two decades before. When ideas run out, just spread one good idea over six episodes, oh and show more cleavage. It works, honest...
Scifi is a genre where imagination should run wild. Weird dystopias, strange worlds, the struggle of individuals to comprehend their existence in other-worldy societies so alien they're hard to comprehend. In mid-2004, I now find myself in a situation where there is no decent scifi left at all. The days are gone where I could be impressed with a series which involves whole alien species and their diverse socialogical situation being shown as lesser known actors in latex masks all wearing the same clothes. Oh, and time travel stories. Again.
Just as well we have CSI. Pffh.