I agree with your comment about "The Conversation." It's one of my favorite films ever. It was Coppola's next film (as a director) after "The Godfather," and I actually prefer it.
Thinking about "The Conversation" reminds me of another great actor -- John Cazale. Before he died from bone cancer at the age of 42, he made just five feature films: "The Godfather" (as Fredo), "The Conversation" (as Stan), "The Godfather: Part II" (as Fredo), "Dog Day Afternoon" (as Sal), and "The Deer Hunter" (as "Stosh"). It's hard to think of any other actor whose film resume was as uniformly distinguished. He was the antithesis of a leading actor, playing homely, Sad-Sack losers.