The kind of musical stinginess you mention seems strangely endemic to movies about singers, don't you think? So few biopics or even films about fictional singers—movies that are purportedly about the act of singing—stop to let the audience hear the complete performance of a song. It's then that you know that the movie is less interested in singing than it is in fame: The song is just there to be used, a means of illustrating the emotional state of the singer or advancing some plot point. Crazy Heart, a movie I know I liked more than you did, was a rare exception in this regard—by the time that movie was over, you really knew your way around the Bad Blake songbook. You'd even heard several of his hits sung all the way through more than once, in different interpretations and performance contexts.
Are there music biopics about real singers that successfully weave story and performance together in this way? In this movie, we briefly see Gainsbourg trifling with an idea that much later will become "Je T'Aime … Moi Non Plus."(By the way, did you get that the record executive who agrees to publish that succès de scandale was played by the late New Wave director Claude Chabrol?) But we never know why he abandons the song then and picks it up later, or what happens in between that changes his approach to it. I'd love to see this movie, and musician-centered movies in general, take the process of composition more seriously as a story element.
Your vision of the Gainsbourg movie as a jukebox musical got me imagining that such a sub-genre existed: What if there were a cottage industry that cranked out jukebox musicals for famous singers—Dylan, Sinatra, Billie Holiday? I'd watch them, but through my fingers, probably, dreading each next small act of desecration by banality. (Walk Hard: The Dewey CoxStorygot so much more right than it's given credit for.) Movies about the lives of musicians can't win, it seems. If they're too literal (does Across the Universe contain a character named Michelle to whom someone sings the song "Michelle"? don't answer that), they set off the cringe detector. If they're too abstract—like Gainsbourg, with its unexplained cabbage heads and mocking masked doppelgängers—they leave the audience craving what it came for: Some face time with the singer and his songs, which presumably we enjoy watching him sing. (Otherwise, why would we be seeing his biopic?)
Nu? You were going to explain about the puppet?