When you get to 88+ areas and the quest content actually starts to become a challenge, and I dont mean long grinds of mindless easy mode stuff, I mean jumping from hell to inferno on d3. Particularly the mantid, those guys hit hard.
Even though I speed levelled through the content the first time (skipping lore) I really liked the fact that it wasnt just a scaled level of monsters as we moved through pandaria, but a scaled level of difficulty. Monsters having realistic health pools as opposed to generic level appropriate ones, meaning that not only do you have to adjust per zone, but you need to have a tactic for each different enemy you encounter, or these guys would tear you to pieces.
Just hope that the playerbase can cope with this and mobs dont start getting nerfed so people can go back to spamming 1 or 2 buttons again. Having to think about every enemy encounter is the breath of fresh air that questing needed to make it part of the game again, not just a necessary chore.