1. Public non instanced dungeons, similar to what we had in EQ, Vanguard, to a degree in ESO

2. More involved quests. If anyone has played The Secret World, you will probably remember fondly the investigation quests, that sometimes took you all over the world figuring out cryptic clues and with no quest markers

3. Something akin to the world raid bosses from GW2, where an even spawned with a towering Godzilla like raid boss where every player could join and complete, with multiple stages and item rewards for contribution

Just some ideas.