Not that Blunt's Tamsin and Considine's Phil aren't also played by consummate actors who needed no billboard-sized hints that California studios seem to think we stupid Americans require to understand deep feelings. The only hints of obvious stereotyping that I saw on first viewing was working class Mona's relative homeliness to rich girl Tamsin's "classic" beauty. Even this is tempered, however, by Tamsin's (later questionable) expression of appreciation at Mona's beauty while wearing one of her sister's dresses. Mona is living mostly a lonesome life, with an absent father and dead mother, and staying with an ex-con brother who has latched onto teh Jesus apparently as a way to rebuild his life. Phil isn't that simple, however, and neither is Mona's new friend-cum-lover, Tamsin. We are given little indication that either are more than what they are initially claimed to be, but here's where I was impressed; instead of laying a trail of breadcrumb clues to their true natures, the habitual fallback of pedantic Hollywood screenwriters, we are given only the lies themselves and characters who are too authentic to go blurting their real feelings in contrived asides hidden from the protagonist. As far as we know until the end, both Phil and Tamsin are completely earnest, and to say any more would betray what I can say is the most complete portrayal of a character showing her strength and integrity that I've seen in years.
As to the sexuality - yes, there's girl-on-girl snogging and a bit of nudity, but, refreshingly, Mona's sexual ambiguity has nothing to do with moving the plot. I can't say this enough. Apart from a telling scene where she satirizes the lovemaking technique of her adulterous ex-lover for Tamsin and Tamsin's own affectation with her sister's supposed death from anorexia, either character could have been written as male or female. Even despite Mona's brother's recent conversion, we are not pounded into the ground by homophobic histrionics. Don't get me wrong, it's important to show the real problem when appropriate, but this is not a movie made specifically to give that message. This is the portrait of a young woman who has real strength and who commands respect. I'll take her over a hundred stereotypically broken, violently insane, sexually indecisive, or hopelessly obsessive teenage lesbians who magically find themselves only after their world crashes around them in a paroxysm of anti-gay harassment. Some girls (and guys) already know who they are and Mona is definitely one of those. Most importantly, I didn't want this movie to end; not because we are only given the last five minutes for cathartic happily-ever-aftering, but because Mona is charismatic, as a character is bigger than the movie itself, and deserves her chance to teach us more about being our own persons.
One last thing. Three of the reviews I have read about the movie harped upon Tamsin's parents' conspicuous absence through most of it and implied how unrealistic this is. Those reviewers must not be living in the same world that I am, or themselves grew up in a "traditional" family and believe that this is still (or ever really was) the norm. I personally had a father who, although very authoritarian, happened to work during hours which would leave my brother and I with a more liberal (or, perhaps, better characterized as weary of trying to be strict from having three older children) mother who basically allowed us complete freedom. Rich children especially have the luxury of freedom afforded by parents who own more than one home and have themselves been given social liberties since childhood.