Bring back massive instances like Blackrock Depths.
Bring back hours-long battlegrounds like Alterac Valley 1.0.
Bring back the thrill of danger in the world.
Bring back World PvP on the scale of Tarren Mill/Southshore.
(1) I don't have 5 hours to complete an instance. It took me forever to clear slabs some days because it was over 3 hours with bad groups.
(2) I get bored with BGs that last longer than 20min, plus I can fit them into those little breaks that happen in between real life.
(3) I like world danger, on that I agree. In vanilla it was kinda hard for a warrior to solo more than one mob and you had to clear an area and pull stuff back to you for fear of aggroing more.
(4) World pvp on unbalanced servers isn't much fun. Faction transfers pretty much gave Horde the victory (4:1) on this server.
Structural homogenization happened with the character classes. Remember back when druid tanks stacked stam as their primary, pallies had AoE abilities and warriors complained? Homogenization also happened by using the same old quests over and over. Just throw a different wrapper on it and sell it. There was also a smaller content for endgame in cata. How many interesting dailies are there? Now, it's pretty much just MF for 4.2, and they're hard to do on more than 1 toon. The Thundermar dailies in 4.0 were at least interesting.