Quote from xSashuhx
Well, I believe what Notch is trying to accomplish is more of a mysterious scary. Which makes sense, considering humans have feared the unknown basically for as long as they have been in existence. He wasn't going for a straight up scary, more of a subtle mysterious and creepy.
I agree, the endermen in my opinion would be more scary as they are now than how you described them, it's not like they're red devils who go around trying to kill you from what I have heard, even in the picture they posted on the main page showed that they were more civilized than the other mobs. Not blood-thirsty demons.