I've said this a lot in any places, so it's beating a dead horse for me, but here they are anyway:

1) Build a proper, real physics engine for the environment. A real 3d-platforming jump and fixed hit boxes.
2) Rework your in-game UI/tooltips to be less TEXTY and more graphical;
---->Put every single jobs' intended rotation in game in a graphical way, with things labeled like they are on the webpage.
---->Explain skill weaving ("These are extra abilities you can use between Global Cooldown skills.")
3) Revise the main menu "orbs"; Specifically why certain things are in "Character Settings" and not "System Settings".
4) Rework job quests to specifically teach the rotation and allow you to test it out/get feedback on doing it correctly. Alternatively add this to The Smith (Options could just be "Current Job Skill Guide")
5) Add more purpose to Open World. Include more things to do in open world that are NOT fates. Minigames (Jumping Puzzles, actual racing, etc; literally just copy Guildwars 2)
6) Next Open Midcore Content- Eureka-sized dungeon(s) with switches/doors/chest/etc where you have to literally delve/search out certain monsters/treasures/paths in a limited amount of time. Certain obstacles cleared might give more time. No bosses rooms but pop-able Eureka-style NMs. See FF11 Dungeons.
7) More Level-free things to do (like Gold Saucer/Ocean Fishing) where people can just goof off -together- without worrying about XP/gear. Casual stuff. Maybe a checkerboard or deck of cards.