Not much, there's some orcs and wargs who die in grizzly ways, which they didn't in the theatrical version. But it's not gratuitous, and so quick, it's more blink and you'll miss it. It's similar stuff to the Rohirrim horseman getting squashed by the Mumak's foot in RotK, just with a bit of splatter.
Plus as I said before the higher rating is for behind the scenes, not the extended cut of the film at all
