Hill Street Blues was a groundbreaking program. It really did lay the basis for the second Golden Age in that it showed people would watch a series with a large ensemble cast with several complicated story lines running through multiple episodes or even seasons. Before that from Dragnet to Kojak TV cop shows were 24 to 26 standalone episodes a season. It might occasionally take 5-O two episodes to solve a crime and McGarrett had as I recall a Chinese Tong Lord nemesis who appeared now and then but basically the plots were designed not to need the audience to pay particularly close attention and you could miss an episode or two and not feel like you had to catch up. Hill St asked for an attentive audience and it did so on Network not Cable which was still just showing movies then.