Honestly I find the movie pretty charming/funny. It doesn't take itself serious, leans into the absurd, and is a relatively fun hour and a half.

There is a a behind the scenes documentary on YouTube about it. There was an edict tfrom the network during season 3 to tone down the urban feel of the show. At the same time, the two leads basically demanded more money before the start of the season. Cooler heads prevailed but everyone on the show was shocked when they got that final script and seeing that Eddie was being killed off. Keep in mind, the ratings for the show were still strong.

The killing of Eddie Torrez essentially killed the audience. Eddie/JC were the show. And it is especially frustrating when you realize how unneeded it was. In the storyline they had already written his character off by having him have to move to a different precinct. And, he didn't die in a multi-episode arc or from a meaningful villain like Ice-T. It was a random villain of the week that blows him up.

Audiences were pissed, and within a few episodes of season 4 it was clear they weren't coming back. The show was canceled pretty quickly into season 4.

The first 3 seasons are fantastic, but as you said, season 4 is unwatchable and a whole different tone/show.