X-Files went on so long there was no sense of discovery and it just seemed up its own behind with conspiracy theory stuff, which made less sense the more we heard about it and was never the main draw of the series anyway. The leads were probably the biggest draw, and it probably should have ended before David Duchovny didn't want to be in most episodes.
Sliders definitely went on too long. What it became was just unrecognizable compared to the solid two-hour movie that kicked it off. Budget dropped, cast replaced with noname actors (sometimes awkwardly playing some version of the same characters), and all of it built on the same foundation: in way too many episodes, the device they need to "slide" gets taken away and they have to have a few low-budget shootouts or fistfights to get it back. The promise of the alternate Quinn appearing in the first episode, a character who appeared to basically slide for the hell of it, wasn't ever realized. Star Trek is proof that watching people explore for the sake of exploring can be interesting at least some (enough) of the time.
