Probably since Kate Winslet, I've never felt an actress deserving an Oscar nomination and win, but Naomi Watt's performance is nothing less than brilliant. This type of emotion, this type of connection both with the other characters and the audience is what acting is really all about. She's deserving of every season award there is. And I have a feeling that she doesn't even care about it. I felt her commitment to the family and to nothing else. Just bravo.
The young children, specially Lucas the oldest of the three, and the husband portrayed by Ewan McGregor are also great, but as another review stated above, the second part of the story that follows the husband's trip to find her missing child and wife was not as emotional or graphic as Maria's journey on the first part. There's absolutely no one to blame for this, it is just that Maria was the one who got injured the most, and as I stated, Watt's performance was on a league on its own.