If I am not mistaken, most people hate Cata for how difficult heroic dungeons was at the start and how the new zones were so disconnected from each other.
I, on the other hand, loathe it for what it did to the 1-60 experience. I know most people love the new quests and how quick you can go from 1 to 60, but I miss the feeling of danger there was in the pre-Cata world.
I miss the *real* Stitches.
I miss how a buff can really mean greater survivability for a leveling character. I loved casting buffs with my priest on players as they run past me.
I miss those Orcs that hid behind the rocks just outside of Lakeshire.
Who remembers Chok'sul?
...and I miss a ton more.