If this movie was just, you know, better, it would be a masterpiece. Denis Villeneuve has many of the elements he needs to make something great. His visual style is top-notch. He knows how to light and shoot a scene, and he's picked actors whose faces he can utilize to the extreme. The premise of the film is tantalizing, and the structure is well-designed. It's really the script that lets this film down. (I'm going to go ahead and make assumptions that the translation from the French and Arabic is good.)
Adapting from Wajdi Moawad's play, he has little scope of what details are interesting, what details are not, and how to write bearable dialogue. He also has an annoying tendency to spell out major plot points to the audience. The film is over two hours long; that could be solved by cutting out some scenes that repeat obvious information and dilute the film's cutting emotional strength.
The film moves between the relative present and 70's Palestine, the site of a vaguely defined conflict between Christians and "refugees" (of what I'm not sure). As we begin, the presumably 20-something twin children, Jeanne and Simon (Mélissa Désormeaux-Poulin and Maxim Gaudette), are parsing out the will of their late mother Narwal (Lubna Azabal). They are given notes which they will relay to their (absent) father and brother, respectively. However, on the way to finding their missing family members, they - and we - will learn more about their recently deceased matriarch.
To say much more about the plot specifics, I would have to dodge more spoilers than I'm comfortable with. So I'll speak in more abstract terms: much of the film from this point onwards is extremely dull. It seems to sincerely believe that thin political soup we've encountered in many other films is going to be interesting. To add to that, we don't get any of the details that are actually helpful/compelling, such as: what was the relationship between the mother and her children before she died? Villeneuve always seems to be worried that he's going to ruin the grand scheme of his film by not controlling the exposition enough. He's so devoted to preservation of the core of the film that he jumps through a hell of a lot of hoops to keep it together; a few too many, it must be said. Finally, the dialogue is clumsy throughout, especially in the abysmal scene that uses math metaphors.
It's sad when you have pretty much everything you need for a success, but botch it with the execution. ("Dogtooth," a fellow also-ran of "Incendies" for Best Foreign Film, showed there are positive results when everything is pushed to, or near, its fullest potential.) In how he tries so hard to lead us down a certain path to not spoil anything, Villeneuve lets many things fall to the wayside. Though many will be horrified/pleased by the twist ending, a good number of folks will also either a) predict it far before intended or b) not appreciate it when it comes to light. The thing about Villeneuve is that he's the right director, but he needed some help with realizing this idea, help he didn't get. C+