Spoilers:
Ismael Vuillard (also the name of the somewhat insane character played by Amalric in Arnaud Desplechin's Kings and Queen) is a filmmaker who has two ghosts: his wife, Carlotta, who had been missing for two decades, and his brother Ivan Dedalus. Dedalus doubles as the main character in the film-within-the film being written by Ismael (adding a layer: Paul Dedalus is the beloved character played by Amalric in three of Desplechin's films).
Within minutes we see precisely what's going to happen, then it takes two and half hours to play out. Ivan, played by the sorely under-utilized and brilliant Louis Garrel, is the more mysterious ghost in a plot line that takes longer to unravel, but this might be simply because his character simply isn't as fleshed out as Carlotta's.
So, by the by, Carlotta comes back, which is what the film is all about. Ismael has been in a relationship with Sylvia (Charlotte Gainsbourg) for two years, and this naturally creates a problem. Aside here: there is more chemistry between Cotillard and Gainsbourg than there is between Mathieu Amalric and either of them.
Amalric is characteristically disheveled, which is to say it appears he didn't bathe once while filming. He wears the same dirty pink/orange pants throughout, his hair is greasy, and his face unshaven. Now that he's in his 50s and not the charismatic s*x-pot he once was, he just looks dirty. It's difficult to see why the brilliant astronomer, Sylvia, is attracted to this character who is an emotional and physical mess. The women are clean and lovely. He not only sleeps with these two, but another woman as well, and references sleeping with many actresses in his films.
The plot line that involves Ivan is weak, weak, weak. Here we've got his *other* ghost, and he's relegated to...the cutting room floor, I suppose. By the end we find out how this parting of ways occurred, but the exploration into Ivan's character is non-existent.
There are some excellent performances by other supporting actors, and while I hate to say it because I am such a fan, Mathieu Amalric is the weak link. He sleepwalks through this performance, like ho hum I'm playing another loony character for Desplechin. Given their long history of mentor / protege --> equals, this is a major bummer.
Overall, I see why this wasn't a well-received film, but I'm personally invested enough in this director and these characters to be tickled by it. I like the intricacy of the plot, though it was too flawed to make this film as excellent as Desplechin's others.
The same material, with this filmmaker and these actors, should have been better – it really is a good story! People leave, we're haunted, and they return as ghosts. In the meantime we go a bit mad. Only an aging Desplechin and Amalric would have this perspective, and I'm going to stick around for the inevitable peace that follows this stage in life, which I assume we'll see in a future film.