These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Family-Unfriendly Aesop: Specifically, Ambition Is Evil. A popular criticism of the movie is that Andy is painted as having gone over to the dark side for having somewhat less time to spend with her boyfriend, family and friends, who are all constantly giving her shit for having a job they don't approve of and implying that she's probably bad at it anyway since they never knew her to be interested in fashion. And in spite of taking this approach, it also passes on the chance to do a Beautiful All Along — Andy gives away most of her designer stuff at the end, but she remains the thinner, sleek-haired, flatteringly-made-up, well-dressed woman she learned to be working at Runway.
It is also worth noting that a key part of Andy's arc has to do with her relationship with her boyfriend, which gets rocky because he doesn't like the ways her job is "changing her" (it doesn't make sense in context either), or that she works such long hours. At one point we see Miranda and her husband arguing bitterly, evidently for similar reasons; and at the end of the film Miranda reveals that her husband has asked her for a divorce. Soon after this, Andy leaves her job and Miranda, tearfully apologizes to Nate and tells him that he was "right about everything".
An Aesop: "Don't become someone you're not just to advance your career, particularly in a 'dog-eat-dog' environment."
Hollywood Homely: This movie tries to pass off Anne Hathaway as unattractive at the beginning, though it may have had more to do with her girl-next-door look and low-budget college wardrobe.
Actually, no, she wasn't meant to be unattractive. Meryl Streep and scriptwriter Aline Brosh McKenna have both said in interviews that this was intended as a comment on the ridiculous standards of the fashion industry.
In one interview Anne even goes on to defend Andy's wardrobe as she wore similar style herself when she was in/freshly out of college.
Les Yay / Foe Yay: Let's just say that what fandom the book/movie has centers around shipping Miranda/Andy. Also, the movie is crawling with subtext; Meryl Streep's performance was extremely seductive.