Police Squad! was a hilarious but short-lived tv series from the minds of the creators of Airplane! and The Naked Gun. In fact, The Naked Gun bases its main character and comedy stylings, as well as some sight gags, from this series.
Each episode has a different opening, with the stars of the show being fired at and them turning around and firing back, sometimes with people that aren't even in the show! They have a guest star every episode, and they always get killed in the opening. Each episode also has two titles, one that is on-screen like a title and one that pops up underneath it like an explanatory subtitle, only the two titles are both completely unrelated.
The humor in the show to be honest is too smart for the average TV viewer. You have to be paying attention to get a lot of the gags, and this works for movies because you're stuck sitting there in a dark room looking straight at a screen. Many of the gags are sight gags (i.e. police carrying a corpse out of a doorway in the background, and it is incredibly long) or like pun gags (i.e. Leslie Neilsen catches the bad guy, turns around and says "Seargants take her away and book her." and then two police officers walk up and he shakes the first one's hand "Sgt. Takeheraway", and the second one "Sgt. Booker") It's an extremely funny, smart show ("Cigarette?" "Yes, I know."), and you have to get the humor to get the jokes. I can see why it fared poorly in the ratings, because most people don't want to think when they get home and watch tv.
Police Squad! was ahead of its time in that there was no laugh track nor a studio audience, and the actors do not indicate when to laugh as they play their parts in complete deadpan. I highly recommend this show to anyone who likes the Zuckers' other creations, and if you haven't seen THOSE, maybe you should check them out.