The only thing worse than a boring movie is a pretentious boring movie. Closer is just that.
It seems like this movie is trying to present a realistic view of the dark side of romance and sex. To me, incessantly asking questions of your partner is not realistic. A large portion of the film consisted of the men asking the women (and sometimes vice versa): What did you do? When did you do it? How did you do it? Where did you do it? After the first hundred questions I didn't care what the answer was, I just wanted these people to shut up already. I on the other hand have just one question: Is this the way real people talk to each other?
In addition these are four of the most unlikeable people I've ever seen in a movie. I couldn't have cared less what happened to any of them. I guess the film is trying to say that they deserve each other. That's fine, they can have each other, but don't foist them on me.