The first two series depict a do-good police sergeant tackling crime in a grimy and impoverished class based system in London and makes telling points about the treatment of people in society at the time. In the later series, the type of cases is more varied and less focused on the under privileged. In the later series, Marriott sometimes takes a major role in solving the cases. It is possible that John Barrie was over committed as he was also involved in Z-Cars at the same time.
In many ways the series was ground breaking with its moralising and technique - it had one of the first portrayals of a siege on TV. The cases were predictable and there was not much tension, however I found the show quite watchable. The quality was OK, however, there were not enough re-takes - quite a few stumbles with the dialog and there was the odd moving wall and stray boom microphone in the shot. Shot in black and white, all 66 episodes have survived.