This movie is really good with Al Pacino (Serpico) giving almost a career-defining performance as he portrays this real-life person perfectly. Serpico kept me on the edge of my seat for the entire viewing and it makes you feel frustrated knowing that it was a true story and also looking at the news today and knowing that this corruption in the police departments is still going on.
If you are a fan of Al Pacino, you need to watch this film and if you are a fan of films like Training Day then this is the one for you. Just understand this film was made in the 70s, so some of the editings can be a bit abrupt and confusing.
Weirdly enough, after researching the true story of Frank Serpico and knowing some of the bits left out of this film, I'd definitely like to see a filmmaker like Martin Scorsese or Spike Lee remake this film with modern editing and acting as some of the side actors are not very good in this film. But otherwise, this is a great film and I recommend it.