Granted, as I am a Stanley Kubrick nut, the following statement is somewhat biased but having seen a lack of critical anaysis of any depth at this node, I felt I had to offer a statement as to what the film meant.

Contrary to the other opinions expressed on this node, I liked the movie. Perhaps it's not a thrill-a-minute blockbuster sensation, but neither were Barry Lyndon or 2001: A Space Odyssey., other arguably excellent movies of Kubrick's.

What then, do I find so charming about this movie? Watching it straight, going into the theater expecting just something fun to do on a Friday evening, yes, you'll find it a bit slow. By the same reasoning, reading War and Peace on the Subway on your way to work might drag a little. The fact is, this movie is made to be looked into and thought about, seen again, puzzled over.

Enough rant. Eyes Wide Shut is a movie about consciousness and perception. He does this first and foremost by showing the main characters in various altered states, all acted out in almost campy exaggeration - filmic hyperbole: there's Tom Cruise and Nicole Kidman drunk at the party in the beginning, the prostitute under heavy drugs, Cruise and Kidman on the ganja weed, the woman who's father dies experiencing Florence Nightengale Syndrome for Cruise - all of this mixed with the constant, powerfully psychologically altering effect of sex and sexual attraction - Nuala at the party, Domino when Cruise goes out, the Daughter of the Rainbow costume shop (incidentally, Nuala was going to take Cruise "Where the Rainbow ends".) and most obviously the Party.
In addition to showing how people's perceptions can be altered and the effects of that, he plays with the audience, making the watcher an active participant in the Drama of confusion. We are assaulted with ambiguous and indecipherable social situations. Like the novel, the situations with which we are presented start out mundane but gradually grow less and less real as the dreamlike state of the film takes over, culminating of course in the massive, masqued ball where no-one knows who anyone else is or what they are thinking - individuals become so obscured behind their masks that their identities and motives leave the watcher thinking What the Fuck?
We are first presented with the straightforward relationships: husband and wife, mother and daughter, parent and babysitter. However, once we get to the party, the interactions become more intense, and slightly less decipherable. While we know that the Hungarian wants Kidman, what exactly Nuala and her friend were planning on doing with Cruise remains a complete mystery. And what the host was doing with the whore at his own party is only hinted at - and assumed - by the audience. The number of unkown elements is taken up a notch. Why did Nick leave Med school? Why is he playing piano halfway across the country from where he lives - and exactly what experience does he have walking away from things?
After Cruise and Kidman fight at home, Cruise leaves for the home of one of his patients who has just died, and here we are confronted with an incredibly bizzare situation, as the daughter of this newly dead man proclaims her love for Cruise, despite her having been affianced to Karl (funny how I can remember his name and not hers). Her wild eyes and nervous manner leave us, and Cruise's character, intensely perplexed.
From here he meets Domino, a prostitute whom he pays but does not end up sleeping with, leaving with the intention of going home - but not doing it. Domino is an interesting situation - the name for the cape and mask combination everyone was wearing at the ball, one might suspect that SHE was the one who offered - inexplicably - to save Cruise's life (warning him against the ironic background playing of Strangers in the Night). But he is told it wasn't her - she contracts aids and goes away - and we are left not feeling as if we know wholly what was going on.

Which is the whole point.

The movie is largely about this perceptual limitation/ alteration that alcohol, lack of sleep, sex drive, anything really can trigger. Innumerable other examples of this exists in the film but I must return to work.