A considerable part of Coppola's reputation as a filmmaker rests on The Conversation, a monochromatic character study of a professional eavesdropper who takes a more-than-professional interest in his latest assignment and gets in over his head. The film has been extolled as a Great American Film, on the severely foreshortened scale with which American films are measured. It won the Palm d'Or at Cannes in 1974. It lost to The Godfather Part II for the Best Picture Oscar.
Who could blame a professional wire-tapper for occasionally being paranoid? Except that Coppola's hero, Harry Caul, lives behind triple-locks in an empty apartment, which is further protected from unwanted entry by an alarm that sounds like a fire alarm, uses pay phones rather than a home phone, keeps his office and all of his expensive and sophisticated equipment (mostly of his own design) in a nondescript warehouse. He avoids personal contact, and frequents prostitutes rather than bother about a girlfriend. He goes everywhere wearing a thin grey raincoat that gives him the unfortunate appearance of peep-show pervert. Why does Coppola make Harry, whom a colleague calls the "best bugger on the east coast", so seedy and sinister? Harry and his equally dismal friends are extremely proud of their expertise and their ability to pry into anyone's privacy, no matter how isolated or impossible to reach. It is a world very far below espionage, which at least has a higher aim - even if that aim isn't always clear.
Coppola was obviously paying belated homage to Michelangelo Antonioni's Blow-Up. He even introduces a mime in the opening shots, echoing the troupe of mimes that frames Blow-Up, who appear boisterously at the beginning and who play the famous tennis match with an invisible ball during the closing scene. (1) Coppola's mime (Robert Shields, who went on to fame as one half of "Shields and Yarnell") is nothing much more than what mimes usually are in the park - annoyances.
Coppola's homage would've been welcome if The Conversation were a better film. Antonioni's hero stumbles onto a murder. In Coppola's film, which is intended to be "existentialist", Harry actively listens in on a murder. Antonioni's film explores reality and how we manipulate it to suit our purposes. Coppola's film is a low-intensity thriller about how one man's cleverness betrays him.
The rest of the cast is a veritable who's who of aspiring 70s American actors. Cindy Williams, memorable for American Graffiti, forgettable for Laverne and Shirley, plays the wife of a business executive whom Hackman assumes is a potential victim (his dream of confessing his surveillance of her is particularly stupid). That she emerges as a co-conspirator was a plot twist that fell flat. Harrison Ford, before Star Wars and Raiders of the Lost Ark, is a completely unsinister threat, doing little more than contribute to Harry's paranoia. John Cazale, who was in practically every other significant film of the 70s (Dog Day Afternoon, The Deer Hunter) is fine as one of Harry's cohorts.
The film closes with Harry sitting in his ruined apartment, after he has destroyed it looking for a bug (a hidden microphone). For relaxation, Harry accompanies jazz recordings on his saxophone. It's a working metaphor, if you will, for Coppola's pedestrian accompaniment of Antonioni's art.
(1) I prefer to interpret Antonioni's mimes as other than metaphorical. They are as much as they seem.