I really missed it when classes were unique. Going into a raid like Karazhan meant that a number of the encounters changed depending on whether I had a mage, a priest, or a hunter or some combination thereof. Shaman totems made a difference. A Pally tank was different than a Warrior tank or a Bear tank. You could succeed with any combination, and it made the game far more interesting figuring out how to use the very different classes as opposed to today's concept of just bring 2 tanks, 3 heals, and 5+ dps and every encounter playing out exactly the same.
I miss the little things that made WoW an MMORPG. Things like different arrows, components for some spells, quests for class mounts, etc. Gathering never really bothered me because it led to getting something of interest...not just gold to buy equipment on the AH. You would run into the opposing faction here and there, and sometimes battles would ensue. Before the cross-realm changes, you would many times see the same person you ran into weeks or months ago. The world felt so much more alive.