I remember back in the early ‘90s, A&E reran his shows from the early to mid 1980s period and many of those were cool to watch, with the guests, etc. I agree with the both of you that the last number of years he was on TV he really was not that watchable, basically anti-Republican stuff that was pretty tired.
Letterman could be incredibly wacky and inventive in his late night NBC show. When he moved to CBS and the earlier time slot, he was basically just phoning it in and not putting in much effort. Part of the reason was the assumption that the audience for the earlier time slot didn’t like weird, edgy stuff. But he also got rich, tired, overprivileged, and lazy.
One of my favorite bits was when he dropped stuff out a 4 story building.
Loss of the Tonight Show gig made him a bitter A-hole, and his move to CBS was just not funny and boring. I quit watching after a couple of months and never went back.