I have to admit, the E3 demo bored me, it was OK but nothing extraordinary, I didn't want to play the game being confined on a dark boat.
The Gamescom demo however...DAMN...That was epic, the scenery and action scenes are just beyond anything else, the character interactions were brilliant too. The scene in the cargo plane reminded me of James Bond, it looked unbelievable.
My only complaint, as someone already said, is that it didn't feel like there was enough "wind", wind effects are quite a big deal, especially on clothes and the noise of air rushing past you, it's just the icing on the cake.