Wow. This is a great film.
Farhadi kept evolving with every new film he made. He still uses a divorce in the film, but that divorce is transformed into a subtext this time in order to apply his own Antonioni-esque plot in a very similar physical setting: the sea, which vastness hides a bloodcurling amount of incomprehensible secrets.
And then again, if we compare both films, we'll realize we are with entirely different universes, and perhaps aren't comparable at all. Truth to be told however, Antonioni's film was a character study of alienation, the disappearance of the character creates a new unspoken attraction between two new leads and becomes a metaphor of the disappearance of the life priorities of oneself's existence, and the affair happens after the disappearance.
About Elly is both thematically and psychologically backwards. That is, the "love" affair was planned to happen before the disappearance, and was orchestrated by a group of friends, mainly by a female third party. Moreover, the disappearance turns the lives of everybody upside down, and this psychological analysis fleshes out the characters. Finally, the intention is not to alienate, but to make the tension as realistic as possible.
"Tension" is a word I use a lot while writing about Farhadi, because the art of his moviemaking consists exactly in the slow escalation of tension. Whereas he will do this two years later in a way few times attempted before by any moviemaker in A Separation with one of the best opening sequences of the decade, here he achieves this by introducing the whole cast in such a natural way that you feel as a part of the group. You literally play, joke, drink and chat with them. Enough time is spent to set a mood and then drastically change it in the second act.
What is very interesting about this mood evolvement is that the plot description already sells the main event: Elly will evaporate from the earth's surface. So the more you get along with the characters' anecdotes, the scarier the idea of somebody disappearing or having an accident becomes. This is proved by the first incident portrayed in the film, which just happens to be unrelated with Elly, but with Arash. The whole situation is so tense, that you start to wonder whether if you'll be able to handle, yes, the tension of the next incident.
Farhadi's most important thematic trademarks are present here as well: the power of a lie or lack of communication can bring destruction to everybody involved, little children have to cope with adult problems that they do not understand (suffering in the process), and one single event, suspicion or differing perspectives towards a single problem are the elements used to create verbal, physical and emotional confrontations between the characters that peel their intentions, personalities, fears and impulses as easily as you peel an onion.
Bravo to that.