Harsh language + violence
First, the positives: the game is gorgeously rendered & atmospheric. By far THE most immersive Batman game ever. The voices & faces of the actors put you in the movie, and the range of options--striking from ambush, stealth, gadgets--finally takes us beyond a mindless fighting game.
Now, the negatives: the language startled me. You will encounter d's and h's aplenty, but be prepared for it to get even saltier with some of the villains (particularly the first big boss, Falcone). It is definitely a PG-13 game. The violence is actually toned down from what I expected, although some of the fear-toxin-induced images could be unsettling for younger players. A great game that even my older kids unfortunately will not be allowed to enjoy because of frequent harsh language and occasional intense images.