We were very impressed with the second installment of this trilogy. You couldn't ask for a better director than Peter Jackson to continue everyone's nerdy adventure through Middle Earth.
Obviously, there are plenty of violence and gore with the wars and orcs/goblins. There are frightening characters that could cause some issues for younger kids, thus the 13+ rating from us. I don't think it's any more frightening than any of the other LOTR/Hobbit films. So, if you allow your children to watch them, they could handle this one.
Will definitely add this to our collection of all the extended versions once it come out.