He gave it 1 star because he hates ambient music (check out his review for Traffic, which is a 5-star score in my eyes). Also, he doesnt watch every film for every score he listens to. Which is a MAJOR POINT, here. Watch the darn movie, and THEN review the score.
I completely gree with you, the score works so well in the film. I loved this because it was so dark and moody - JUST like the film, yet he slates it for being mood in the review. Again, WATCH THE DARN MOVIE and then rate it. You can just give ambient stuff 1 star cos you hate it, what kind of unbiased review is that?!
I found Michael Clayton to be an intricate and fascinating score, and it deserves a lot more than 1 star. It fits the film, it carries the emotions, it's more than serves its purpose. And well done Academy for nominating it, its great.