I'd list all of G-T's Big Three Panel Shows: WML, TTTT and IGAS in their original versions.
Not that they aren't great; the fact that two of them were in new versions in 2000 shows that. But the originals had looked tired by the late 1960s when CBS kicked them off.
One of the reasons for the continuing success of such shows as MASH, ER and Cheers was that just when a character started getting unbearable, there was a change and a new dynamic. Maybe it wasn't planned (death, contract walkouts) but it juggled the interaction, rather like Looney Tunes moving in Daffy Duck to play against Bugs Bunny.
You look at the syndication success of TTTT (Moore) and WML (Bruner/Blyden) and you see that a shakeup seemed to help. Getting Bill Cullen (who?) also helped TTTT's syndicated version. IGAS, on the other hand, was the weakest of the three games, and wasn't as shaken up (Steve Allen had hosted the network version for a few years) so that wasn't as successful.
I realize none of this explains Bob Barker still doing the same show at 80 that he did at 50, but that's another post.....