I don't think anyone with sane mind would be able to say that William Friedkin's The French Connection is an overlooked movie. It's a classic crime film, and it's a classic in its own right. Everyone knows the hectic chase scenes, everyone knows Gene Hackman as Popeye Doyle, the narc cop prone to violence.
But you should see the film on big screen. I'd seen the film I think twice before yesterday, but now I had the chance to see it projected on silver screen from 35 mm print. The print was faded and scratchy, but boy, did the movie deliver! All the cinematic stuff in The French Connection was designed to work on the big screen, not on television. I remember that I had really not liked the film when I saw it earlier, but now I realized it was because of the wrong media. Friedkin uses lots of pans and zooms that don't work well in television. There are few close-ups, so we don't really get inside the characters. It's more like a documentary we are watching, even though it's a very entertaining and exciting documentary.
The soundtrack by jazz trumpetist Don Ellis is also great. I like the way Friedkin uses music and other sounds in the film, mixing them rather freely with each other.
More Overlooked Films at Todd Mason's blog.