I especially enjoy the old time radio comedy writing. The writers did not have the luxury of falling back on sight gags or being augmented by visual slapstick, yet it was frequently very witty.
Depending on the show in question, they had a slightly deeper challenge---timing and placing the aural gags and audio slapstick, which is often a lot more difficult to bring off successfully. With the right sound people, attuned to the nuance of the characters and the rhythm of the dialogue (the sound people working such shows as Fibber McGee & Molly, The Great Gildersleeve, The Fred Allen Show, for example), the aural gags enhance and amplify the verbal humour, and the best comedy writers knew how to work with those as characters in their own right.
They had a challenge even deeper than that, if you take seriously the observation of one of the genre's absolute masters, Goodman Ace (Easy Aces): "A lot of times, on the air, I noticed comics in a sketch do a joke that destroys the character because it gets a big laugh." You could say that that knowledge was a key in making the quieter comedies---Easy Aces, Amos 'n' Andy, Vic & Sade, The Goldbergs (though it was always an open question whether this show was as much if not more a drama), Lum & Abner---endure as they did; to a one, almost, any of them that were converted to the half-hour sitcom format (as all but The Goldbergs were in their final radio years) lost too much in the conversion.
Ace himself conveyed the frustration when describing what CBS did to a show he'd worked up for Robert Q. Lewis (an occasional Easy Aces/mr. ace and JANE guest performer): "I give them a good, tight fifteen-minute comedy show and what do they do? Bring in an orchestra and an audience. Who the hell said a comedy show had to be half an hour? Marconi? Ida Cantor?"
An irony: Fibber McGee & Molly went the other way beginning in 1953: from a half-hour show with audience and orchestra to a fifteen-minute offering without the audience and orchestra. Having everything that survives of their show (and a boatload of it has survived), I can tell you the fifteen-minute, semi-serial version of the show is just as funny as the original half-hour. And the absence of audience probably allows the joke to grip a little more firmly, if a little more gently.