This thing is a total farce and a comedic masterpiece. Utterly unique, one of the most interesting movies I've seen in some time. An instant favourite, which is apparently misunderstood by many, judging by the reactions on this website.
The two central performances are marvelous; the movie probably wouldn't work too well without them. The script certainly feels like Cocteau wrote it, with all its surrealism, and even melodrama. Melville's direction brings a grounded quality to it that Cocteau may not have been able to pull off; the serious tone of the film, aided by over-the-top blaring of classics from Vivaldi and Bach, is what makes this so effective as a satire of more prestigious dramas with complicated love stories.
A flick blowing away all expectations is the most exciting thing that can happen to a movie viewer, and LES ENFANTS TERRIBLES did just that for me. This definitely cements Melville as one of my very favourites.