There's a horrible flaw in the conception of the main character here that keeps the movie from being really great, but there are enough good jokes and funny performances to make it well worth seeing.
Anne Hathaway stars as Andy Sachs, a wholesome midwestern girl just arrived in New York hoping for a career in journalism. Instead, she lands a position as assistant to Miranda Priestley (Meryl Streep), editor of Runway magazine, and as such, one of the most powerful women in the fashion industry. Andy does not follow the world of couture, and has never even heard of Miranda before being hired, so she has no idea that Miranda is a tyrant of a boss, burning through assistants at a dizzying pace.
It doesn't seem likely that Miranda will put up with Andy for long. Her clothes are wrong, she's not pretty enough, and she doesn't know the industry (Taking a phone message, she asks, "And how do you spell 'Gabbana'?"). But after the inevitable makeover sequence -- very nicely edited to show us a dozen or so of Andy's new looks in one walk to work -- Andy gets down to business and sets out to become a great assistant.
There are no surprises in the story; we've seen all of this before. Andy's determination to meet Miranda's impossible demands ("My twins want to read the next Harry Potter; get me a copy of the manuscript.") means that her relationships with best friend (Tracie Thoms, who deserves better parts than this) and boyfriend (Adrian Grenier, who doesn't) will suffer, and Andy must eventually choose between life and work. (In a way, it's Click: The Chick Flick.)
The problem is that Andy is a passive wimp. She never fights back or challenges Miranda, and the movie desperately needs a good verbal battle between the two. Instead, she simply takes all of Miranda's abuse with good spirits and an occasional fit of whining to her friends. And at the movie's climax, when the formula requires that she ingeniously save Miranda from some awful fate, she's such a weak character that even that opportunity is taken away from her by the script.
Hathaway does all that can be done with the role. It is one of the standard bits of Hollywood nonsense that the girl who needs a makeover was already pretty damned attractive to begin with, but I think that's part of the joke this time; everyone at Runway is so caught up in high fashion that they genuinely can't see Andy as pretty until they see her in couture.
The movie's real attractions, though, are in its supporting cast. Stanley Tucci gives the gay sidekick role more dimension than it usually gets; Emily Blunt is marvelously brittle as Andy's co-assistant, who sees her primary position vanishing as Andy works her way into Miranda's good graces.
And as Miranda, Meryl Streep is magnificent. Miranda is not one to fly into furious rages at people; she simply nods or purses her lips before dismissing them -- "That's all" -- almost under her breath. Streep looks fabulous here, and it's an interesting choice to show a woman in the fashion industry who embraces her maturity; her hair has gone silver-white, and it would never occur to Miranda that it needed to be colored a more youthful shade. Streep lands every joke and gets every laugh to be found in the part.
The movie's a lot of fun, and it's a solid piece of entertainment, but I can't help wonder what might have been if Andy had been written as someone capable of giving Miranda a real battle; that could have been an all-time classic.