This is my most favorite video game of all time! It is so beautiful, and awe-inspiring. This is a somewhat violent, slightly gruesome game, but is not inappropriate, for the monsters are non-human and their blood (if any) is black or green. However, this is an addicting game, which may cause teens to play it for hours or beg to at least. And, there are some parts that keep you on edge when you know something bad might happen, so just be aware. I would recommend, even if you're thirteen, playing the beginning of the action-parts with a friend, if you haven't played monster games before, because I was so on edge and scared of the monsters at first, but it took a day to get used to them. Anyways, this game is appropriate, awesome, and THE best.
(P.S. very mild bad words, like idiot, shut up, etc.)