I must admit my French is a little rusty and I could have done with some subtitles so I was having trouble following the first half of the film on DVD. I borrowed it because I think Daniel Auteil is a good actor and had no idea what it was about except something about a man who lives a lie.
I watched it through to the end and recalled reading so many similar true stories in the last few years on cnn.com that I really got a shock by the end. As one of the scriptwriters comments in the extras on the French edition of the DVD says, "those scenes brought the film back into reality".
I found some of the editing a little jarring but perhaps that was intentional. It all makes sense in the end. Interestingly the producer - again, on the French edition of the DVD - said that she just wanted to follow the main character through his life without judging or diagnosing him, so perhaps those of you who know something about psychiatry will have a different perspective.
Stick with it, revel in the details of the film, and hug your family tightly afterwards.