I will go with:
1. Lore. It needs hella more lore, but WC didn't have much lore in beginning neither.
2. Smoother cast bars, it's just annoying.
3. All-Enemies Nameplates with aggro bar.
4. Threat meter.
5. Less buttons. As a Cabalist/Inquistor I got 12 buttons to press and I am just 16. Less self buffs, my Justicar/Druid/Shaman needs 7 selff buffs and one pet activated before I can do shit.