I realized the other night that I have quite possibly the strangest complaint about Wrath of the Lich King possible: There is nothing that you can just go grind if you want to do something mindless. By grind, I mean endless killing of mobs for some minor gain. One of the biggest reasons I play WoW is for social purposes. I play WoW with a lot of my friends, and sometimes when I log on I just want to use the game as glorified IRC while I stab things.
This worked well in The Burning Crusade, because there were a lot of quests that required you to pay attention to what you're doing, but there were also a few reputation grinds that you could do just by murdering lots of mobs, which was great for those lazy days. Zaxxis Insignias, Warbeads, Marks of Sargeras, all of that stuff. If I didn't want to do anything complicated while I chatted away in guild chat, I could just round up a bunch of mobs and killify them, and I would still be making progress toward some game goal.