Radio Four must be unique. It's an all-speech channel. I can't imagine a commercial version because I don't imagine the audience figures are particularly high, so it would never survive on advertising alone. It broadcasts a wide range of material across such things as documentaries, arts, media, light entertainment, comedy (light entertainment covers panel shows and sitcoms and sketch shows.) as well as soap opera (The Archers would fall into this category. It's supposed to be the longest running drama or soap in the world, running for something like 65 years. In fact, it's one year younger than me.)
I got hooked on adaptations of books which were (and probably still are) broadcast on Radio Four. For example, some of Daphne Du Maurier's novels. which lead me to read many of them, particularly 'Rebecca' and 'Jamaica Inn.' I think I'd written them off as being somewhat female-orientated (which perhaps they are, to some extent.) but then, once I'd read them, I discovered that there was far more to them, particularly 'Rebecca' which is really gripping and has a mystery about it. She does atmosphere and character really well. Definitely page turners. The books have been adapted for both radio and television, and of course 'Rebecca' was famously made into a film by Alfred Hitchcock, with Laurence Olivier in the role of Max DeWinter. She also wrote another, the later novel which was called 'The House On The Strand' which was done well on the radio. There's something about a radio adaptation, you have to concentrate more than with a visual medium. There's no way you can get away with the scenery dominating, flashy camera-work etc with a totally aural adaptation of course.