French Connection II is a Frankenheimer first, and a sequel second. It's different, but legit. Doyle's character is explored more fully, and he has some poignant moments in his obsessive drive, his misfitness, his loneliness. He'll never fit in no matter what. The story is exactly right. I agree that it complements the first film. I like how it opens with a practical joke. I like the gritty ambiance of Marseilles; not even the French capture France the way Frankenheimer does. Every decision Frankenheimer makes -- such as to do a foot chase along the waterfront instead of a car chase -- was correct, except perhaps for allowing Hackman to grandstand with the chicken wing in his hand. That went on too long. I love the last shot.
I saw a preview for critics in Brooklyn with Frankenheimer in attendance. During the q & a afterward there was a woman critic in the audience who kept standing up to ask if Frankenheimer's intention was to expose Popeye as nothing more than a beast because of his dialog about hamburgers with bloody ketchup. Frankenheimer finally told her to sit down and shut up.
I miss movies like this on the big screen, I really do.