Yeah, this is only really fun if we pick shows that were somehow successful despite how lousy they were. Canceled and/or obscure shows got what they deserved already, right?
Now the animated "Laverne and Shirley in the Army" ran more than one season and would hence qualify, but somehow I had an urge to go after more elusive prey than that or "A Shot At Love With Tila Tequila."
I think "Small Wonder" comes up a lot in these sorts of discussions, and that's okay.
I have a strong urge to mention shows that really run for a long time and make money and such but are just so spectacularly awful. Shows that seem like they are over long before they stop making new episodes, that no one ever talks about as soon as they are over except to mention how awful they were. "According to Jim." "Dharma & Greg." "Ally McBeal." That last was some sort of pop culture phenomenon while it was on, then ratings nosedived, and by the time it was over it was like a shameful secret that anyone had ever gotten excited about it. Man, was it bad.