I've just started to listen to these, big fan of the TV series and was given these as a Christmas present. They are superb, the show really translates well to the radio. James Beck isn't in many as he died quite early on during the recording of the radio version so Graham Stark stepped in for a while, then Larry Martyn took over, who is better than Graham Stark in my opinion.
I highly recommend these for any fan of the show. The episodes are radio versions of what we have already seen on TV, but they are just really great.