A lot of them are hard, but none of them are terribly impossible. They really give a great sense of accomplishment, especially if you're like me and made it a personal goal to get in the top three ranks for each mission, which requires an immense amount of ingenuity and unorthodoxy.

I still pull the game out from time to time just to play the Ninja missions. Running and jumping all over the place, slashing entire crowds of guards in half... That's what it's all about. They really ought to include a mode like that in one of the future games. "Raiden (Ninja)" was a pale imitation.