Tasha Robinson argues it's a happy ending:
Essentially, this year’s Best Picture nominees go beyond the message "Things are going to work out fine," and head well into the realm of "Things will work out no matter what you do." And this year, at least, any film not toeing that line got shut out. Consider films like Contagion, Meek’s Cutoff, Weekend, and Shame—all potentially strong awards contenders that struck a chord with critics, but not the Academy, and all specifically concerned with characters trying to come to terms with past events, then figure out their futures. In particular, the stellar but Oscar-shunned Martha MarcyMay Marlene and Take Shelter directly address characters concerned with their family history and their personal history, and trying to understand and accept the past and keep it from poisoning the present.
But all six of these films have ambiguous, difficult endings that suggest the future is uncertain, or threatening, or exactly what it is: a vast unknown. This year, at least, that idea is entirely unwelcome in the Best Picture category.