Was Parenthood in those last 20 years? That was a great movie. But I agree about Martin. Something about him makes me believe he thinks he’s smarter than he really is.
I think that the overly arrogant facade is just a part of his schtick. Watching some of the recent give and take with some of his pals on SNL was enlightening.
Martin is a pretty good actor, IMHO. Most good stand-up comedians are...they have the timing "thing" down already and can read other people (like actors onstage) well enough to play off them. Robin Williams has done some interesting non-comedic roles. Tom Hanks got his start in stand-up and throwaway comedies, as did Val Kilmer.
Will Ferrell, Jack Black, etc are physical comedians...that's why they get old so fast, IMHO. Also it's why Belushi was as successful as he was - played bit roles in most of his movies so that people didn't get worn out on him.