The quest changes seem the most important to me:

A Realm Reborn changes (A Realm Revamped?)

-Streamlined MSQ quests

-Approximately 13% content removed

-Other quest content streamlined, much less grindy/bloated and less steps, better for new players

-EXP boost and more gear rewards from quests. No need to do side quests to reach level 50 and beyond for HW.
That's going to be major in drawing in new players. ARR has been by far the biggest turn-off for any newcomer. We've all said and/or seen in Novice chat, the phrase "stick with it, I promise it'll get better in HW!".