I'm not sure what went wrong with this Truffaut film. Francois Truffaut was usually a reliable director/writer but his instincts really deserted him on this film. The Green Room, is about a man's obsession with death. He constantly dwells on death and finally creates a memorial to people he knows who have passed on. This is not exactly going to be a fun film like Day For Night.
In fairness, this was clearly a very personal film for Truffaut. He plays the lead and unfortunately he does not do a very good job as an actor. I can't help thinking a better actor would have helped this film's theme about the effect the dead have on the living. Playing opposite Truffaut is the actor Natalie Baye who is sort of his partner who has an equal obsession with the deceased.
The running time is 94 minutes and probably nobody would want it to run a minute longer. Truffaut wrote the screenplay.