Most cruel twist
How could Anna love Sean (dead husband) that much when he did not love her at all? Yeah, I know he cheated and hid it well and she was totally oblivious to that. But one can only love someone devotedly like that if the other returns the love equally. Sean could not act so well while marrying to Anna but was so much in love with Clara. (He did not even read Anna's letters and gave them unopened to Clara - what an ayhole!)
Such a devastating twist near the end of the movie (when Clara revealed the affair to young Sean). I think it was so cruel for the audience. They thought they were watching an everlasting love between a husband and wife. A love that still exists long after one has died. But then they realized Sean was such a low-life cheat. All Ana's love was just a total waste of devotion. She wasted her life for him.