Megan miscast
In the novel, Megan is described as being almost irresistibly hot. I don't think bennett is hot. I think she's not thin enough and not pretty enough to be irresistible. She's good looking (not my type), but the Megan character needs to be almost supernaturally beautiful. Whenever I see Jessica Biel in a movie, she's almost too gorgeous to watch. I can't follow the movie. Megan needed to be like that.
In the movie (IMO), bennett is the LEAST attractive of the three main women (Blunt, Ferguson, Bennett), and it's not like she has an enchanting personality or dazzling brain. In the book, she's described as being stunningly gorgeous.