When I was 12 it was one of my favorite books (by Peter Maas), and shortly thereafter I saw and liked the movie as well. On this viewing I was struck by the excellent understanding of the culture of corruption, the notion that the mayor is beholden to the police who can threaten to shirk, the performance of Al Pacino, and the wonderful scenes of early 1970s New York City (yes that is Soho you are seeing).
The last quarter of the film should have been shortened. And for all of its attempts to be a politically correct film, the degree of casual racism and sexism still is astonishing to the modern eye, specifically how either black criminals or attractive women are shown on screen.
Nonetheless recommended, and in particular as historical backdrop for understanding 2020. Here is a John Arnold thread on the primary of culture in police departments. And here is the police response to the recent protests.