Just saw it. Here are my thoughts:
This definitely is a film that isn't for everyone.
Mostly, because it does deal with uncomfortable and taboo subject matter... And I don't mean the deviant sexual acts/activities that go on. I am talking about the things (adult) couples do and do not talk about in terms of their pasts, their wants/desires/dreams, past lovers... And forces people to ask whether or not they (as people) do in fact want the whole truth and nothing but the truth...
Or is that some kind of politically correct manatra we've all adopted to make us sound better since if we knew half of the secrets that our significant others kept (keep)... We'd probably react just like any of the characters did to varying degrees: Depressed, desperate, intrigued, exhuasted, turned-on, turned-off, disgusted and relieved... All at once.
I think the most real of the characters was Larry (Clive Owen) as far as portrayls of males go.
Yeah, he was interested in the "down and dirty" details of what went on between Anna and Dan... But like he said, "That's because I'm a f-cking guy!" -- Because it is true, no matter how "evolved" and "sensative" guys try and pretend to be (I am one, so I can say this

)...
But it also goes deeper than that in that if we (guys) know the details... It does take the sting off somewhat AND it makes the events/consequences more "real" in the sense that we
can move on... Like his "deal" he struck with Anna before she would sign the divorce papers.
Men have a much easier time moving on than females, supposedly... And I think Mike Nichols was actually challenging this gender stereotype, or else Larry wouldn't have done what he did AND have gone to see Alice (Natalie Portman) at the strip club (for those who've seen the film, it all makes sense).
Everyone, Julia Roberts, Clive Owen, Natalie Portman and Jude Law all gave Oscar and Golden Globe worthy performances, so I would not be surprised if we see their names multiple times for supporting, or perhaps best actor/actresses.
If anyone gets a supporting actor... I'm guessing Clive Owen... And for supporting actress Julia Roberts (just because I do think her performance is better than Portman's in terms of material and screentime).
In closing, I can see why some people like the film and others don't.
I think the time shifts are definitely disorienting in a drama like this as is some of the "on-the-nose" dialogue -- that I now realize IS on purpose -- But it has its interesting moments and definitely treats its subject matter in an adult, no-holds barred kind of way and I did find that aspect the most refreshing considering that because this has A-List stars, it could have been easily dumbed down to get a broader audience...
But it didn't. I give it credit for being the film it is, but like someone said, I wish there was just a little more background to the characters, so audiences could invest in them a little more and feel for them because in the end...
The characters aren't really "nice" people... And you are glad that you are observing them as a third party. But that is the genius of the film (and play) in that this probably IS how most people really are whether they want to admit it or not.