I think it's the manner of torture (straight up murder, waterboarding, forced rectal feeding, threats to rape people's mothers and children, sexual assault, etc.) that surprises people. And the fact that it was all pretty much counterproductive and unnecessary. Which, again, doesn't surprise some of us, but is still shocking / depressing, and was basically covered up.
From the Prez:
"Nobody can fully understand what it was like to be responsible for the safety and security of the American people in the aftermath of the worst attack on our national soil."
"One of the things that sets us apart from other countries is when we make mistakes, we admit them," he said.