I'll start out.
"All in the Family" had some pretty good spinoffs -- most notably "The Jeffersons", "Maude", and even "Good Times" which spun off from Maude. You could even say "Archie Bunker's Place" was a spinoff, though it was more a continuation.
But then there was this abomination:
"Gloria" was a lame attempt to give Sally Struthers a starring role via her fairly uninteresting Gloria character. It was hard to notice during All in the Family that Gloria was uninteresting, because she had a well-defined and specific role. She was a good supporting character, and Struthers did a good job playing her, but centering a show around that character had fail written all over it.
It was like a depressing, uninteresting version of "One Day at a Time".
Also, it bothered me how the show was built around Mike/Meathead leaving her for a younger woman. Mike was a loudmouth jerk and an ungrateful freeloader, but he was portrayed throughout the series as being a dedicated husband. (Later, when the couple split up on "Archie Bunker's Place", it was revealed that Gloria cheated on him -- a plot which was ignored when the "Gloria" series started).
Anyway, no surprise that this thing flopped.