This was an absolutely brilliant film! I went to see it last week and was moved by it so much that I went again. Oddly enough, I found it a lot more emotional to watch the second time, even though I knew the outcome. I have to agree with the majority here who said Naomi Watts and the boy who played Lucas were outstanding. Not to mention the CGI and sound. I'll put the rest in spoilers regarding the details...
Having said that, this really is a fantastic film. Superb acting and direction. The story itself is horrifyingly remarkable - it would be a tad unbelievable if you told me it was fiction.
TIP : Have a decent supply of hankies