"Barney Miller" is an example of a show that started off as a very good show, was given time to grow and find its rhythms, and became one of the best sitcoms that television has ever seen. At first the show brought us Barney at work and at home, dealing with his wife and kids as well as his duties as a N.Y.P.D. captain. But by the time the second season has begun, the show was focusing almost exclusively on two rooms at the Twelfth Precinct: the detective's holding room and Barney's office. The show rarely left those two rooms for the rest of its run, and it didn't need to; the goings-on in those two rooms among Barney, the detectives, and an assortment of citizens of the Twelfth Precinct, both upstanding and nefarious.
"Barney Miller" had the benefit of sharp writing and an ensemble cast that worked together like a well-oiled machine. Each detective was a well-defined character who over the course of the series' run we came to know intimately, and we got to know a lot of the citizens who regularly showed up at the precinct house, including a gay couple at a time when gay characters were very rare on network television.
It is fortunate that ABC allowed "Barney Miller" to find its feet and become the critically-acclaimed show that it became. It's too bad that few networks are willing to let that happen any more. But "Barney Miller" is evidence of how such patience can eventually pay off.