This movie is a great adaptation of a novel by Lauren Weisberger, in my opinion much better than the book and that is truly rare.
Ok, the book was kinda.. crap. But the movie took what was good in it and gave it to Maryl Streep.
Without Meryl Streep, The Devil Wears Prada would get maybe 2 star rating, (probably 1..) but because of Ms. Streep giving such a great performance it is reason alone to see it.
I especially liked the way that, as Miranda, she never raised her voice above normal speaking level. Streep has said she based this mannerism on Clint Eastwood, who as Dirty Harry talks very quietly but still intimidates. (so, do you feel lucky? punk!)
This made Miranda much more interesting than the stereotypical, screaming gorgon she could have become. And she is so deliciously devilish that you want her in every scene, but we'll settle for a supporting actress nomination come February in a movie that would have essentially been Pricess Diaries 3 without her.
The film is just too long, however, primarily because the director feels obliged to explain everything -- every plot point is rendered obviously and painfully clear, and nothing left open for interpretation. That said, we're spared the "perfect ending" and left with a heroine who can truly stand on her own two feet, and in any shoes she might desire.