Were Mr. Simon’s insert-flap-A-in-slot-B jokes ever funny? I remember chortling at them as a boy, but now they mostly leave me cold. In fact, the whole first act of “The Odd Couple” feels less like a comedy than a set of instructions for making an audience laugh....
This is one of the reasons why the TV version of "The Odd Couple" (with which Simon had no involvement) is so much better than the play or the movie. Simon's original "Odd Couple" is essentially a collection of jokes. Some of the jokes are good, some aren't so good, but all of them feel like carefully scripted, carefully arranged jokes with tick-tock rhythms leading to a punchline. The TV series, created by Jerry Belson and Garry Marshall, was character-driven, not joke-driven, and mined most of its humor from the characterizations of Oscar and Felix and the difference between them -- in other words, from all the stuff that Simon set up in the play but didn't really follow through on.
Simon's characters have no apparent lives beyond the confines of the one set; references to Oscar's job, or Felix's job, are offhand and minor, and they have no apparent interests or hobbies. With the TV Oscar and Felix, we know a lot about what they do for a living, what their interests are, what they think about various things, and much of the humor comes from that. Simon's Oscar Madison is a sportswriter because that's a convenient plot device: he had to do something that he wouldn't require him to dress well or act refined, and which would explain how he affords a nice apartment, why he's often home during the day. Marshall and Belson's Oscar Madison is really a sportswriter; his job is the vehicle for stories and jokes. Simon's characters are automatons; Marshall and Belson's characters are people.
Interestingly, according to Garry Marshall's commentary on an episode he and Belson wrote for "The Dick Van Dyke Show," Carl Reiner did not want to hire them for that show because he thought they were wisecracking New York jokewriters who wrote jokes instead of stories. Translated into the terms of this post, Reiner didn't want anybody who wrote Neil Simon type material. Marshall (an annoying personality, but a smart comedy writer and an interesting DVD commentator) says that Reiner taught them the importance of putting story and character first and of not writing jokes that aren't related to anything, and they carried those lessons over into their subsequent work (like "The Odd Couple"). This goes a long way, I think, toward explaining why situation comedies hold up so much better than most of the Broadway stage comedies of the same era: the people who wrote for character went West, and the East was dominated by people like Neil Simon, who mostly just wrote jokes.