It's interesting how tastes in humor change. I remember when
Chevy Chase was very funny. I don't think his style of humor ever changed, but one day it just wasn't remotely funny anymore. There was a hint of its impending failure in Modern Problems above, in 1981, but it wasn't obvious until Spies Like Us and Three Amigos in 1985-86.
I think his last really funny movie was Fletch, 1985.
Edit: And remember his talk show? It was terrible. Almost as bad as the other short lived one that Charles Grodin had.