So far, whole legendary quest line from Pandaria, and now from Draenor. I don't understand what's the reason exactly.
If you make a new char, or start WoW now as new player, you lose one of the best quest chain from the expansion. I don't get it. Is only for that achievement so much noise or what? Seriously, elitists can take a break, I am taking about a beautiful game here chopped with no real reason.