I watched this movie Saturday night with my wife and another couple. My wife and I are big fans of the Cohens, and were looking forward to the movie despite the scattershot reviews.
I would say that it is a good movie, if not terribly entertaining. The Cohens seem to be exploring the meaningless-ness of life theme that they started developing in No Country for Old Men. In No Country fate was arbitrarily determined by a homicidal madman. In Burn After Reading, the determinant of fate is a CIA beaurocrat who bases life and death decisions on the amount of paperwork invovled.
It is hard to create a conventional story based on a nihilistic viewpoint. If your aim is to show that nothing really matters, denoumont is out the window. This was true in No Country and it is true in Burn After Reading. The former was more entertaining because there were, in a sense, 'good guys' who you wished to see survive and who struggled against the menacing automaton, Anton Chigurh. In Burn After Reading the characters, although realistic, are nonetheless personally preposterous. You really can't like any of them, although they are too stupid to dislike. They are almost like pawns in a game moving inexorably towards their doom, which is perhaps the whole point.
A complaint: it seems that graphic sex scenes are now de rigeur in 'artsy' movies. To the point where the rating explanation is 'suggested sexuality' when the image is of a sweaty man, heaving and grunting over a woman while both are clothed only in bed sheets. It's really slightly more than suggested, which implies some imagination is required.
So, as I said, it's a good movie if not entertaining. If you read the review and it sounds interesting, I would suggest it (minus the heaving). But if you're looking for a few laughs, look elsewhere.