1. Better bags. Items are auto-sorted.
2. Your abilities can now all fit on a single action bar or two. It's conceivable to actually be able to use all of your abilities in a fight now, as opposed to half of them never being touched in any situation.
3. Ten more levels, including a new talent level 100 spell.
4. Seven new gigantic zones to explore, quest, and enjoy the lore and art in.
5. New character models for everyone to gaze upon.
6. New dungeons and raids.
7. No more daily grinds.
8. Smaller numbers.
9. Healers having the time to heal people because they don't die instantly anymore.
10. A new soundtrack.
11. The added power necessary to go back and solo old content from Wrath/Cataclysm/Mists of Pandaria. This includes stuff like Onyxia, Zul'Aman, Zul'Gurub and other dungeons that were upgraded to higher levels of difficulty and became unsoloable up until now.
12. A level 90 boost for those who don't want to do the same old content again.
13. Combo points stay with your rogue or feral druid even when you switch targets.
14. Paladins don't have to constantly renew Inquisition, Rogues don't have to constantly renew Slice + Dice, Druids don't have to spam lifebloom, and many other quality of life improvements. Warriors don't have to constantly shout. Death Knights don't always have to be blowing their horns.
15. Warriors can now dps while still using a shield. You don't have to switch stances in order to maximize dps, you can just stay in whatever stance you like without penalty.
16. No more silly quests that are irrelevant to the overall plot. You'll be actively involved in the heart of the story from beginning to end, and the quests will properly utilize your character's gameplay elements and not just be random nonsense.
17. No longer must you gain an exact amount of hit, expertise or haste in order to maximize dps. Reforging is unnecessary and thus removed. New, more interesting abilities like versatility (for hybrid role users) and multistrike (for cool graphical effects) have replaced them.
18. Hybrid classes don't have to collect twice as much gear as everyone else at twice the cost in time and effort. Your healing plate turns into dps plate when you switch specialization, or tanking plate, or whatever you need it to be, and vice versa. People can now realistically change their specialization from one moment to the next, because their newest and best armor will support them either way.
19. Personalize your Garrison for cool bonuses.
20. Ambush can be done from in front, because it's too much work to walk around behind someone while stealthed, plus works well with shadow dance.
21. Death Knights are ridiculously overpowered balls of pure awesome.
22. Marksmanship Hunters get stronger the longer they stand still.
23. Fire Mages get to actually cast fire spells, Ice Mages stick to ice spells. What a sane world.
24. Discipline Priests and Mistweaver Monks can dps while healing simultaneously. That's hella cool.
25. Shaman Totems are actually fun. You can summon a Storm (Air), Fire, and Earth Elemental to fight for you as pets with their own abilities directly under your own control.
What I'll be Playing: Blood Death Knight, Retribution Paladin, Marksmanship Hunter, Elemental Shaman, Fire Mage, Assassination Rogue, Mistweaver Monk, Discipline Priest, Balance Druid, Protection Warrior and Demonology Warlock -- to start with. :).
What this expansion still lacks:
1. Improved models for armor. Textures look spray-painted on.
2. Better looking rocks and trees. The "world" in World of Warcraft should look better.
3. Another class. The new class should be a 'Tinkerer,' who relies on engineering and alchemy devices to get ahead through external equipment instead of internal training.
4. Two more races. Dryads for Alliance and Naga for horde.
5. A final showdown with Sargeras and the Burning Legion.
6. A final showdown with the Old Gods.
7. More plot development for Gilneas and the Forsaken. Where are they headed now?
8. A new region to fight Sargeras in. Perhaps we go to the demon's home world?
It seems to me that there's a lack of new real estate for people to explore in WoW. Azeroth has reached full explorability since Mists of Pandaria. Now we've covered Outland twice. We've even explored all of the elemental regions in Cataclysm. Exploring new regions is the most fun part of WoW, so it's essential that each expansion have an expansive new world map to journey in. As such, I think one last expansion, where we take the war to Sargeras and go to the home base of the Burning Legion, with all the added features just mentioned -- 2 cool new races, a new class, and wrapping up all the lingering plotlines within the alliance and horde, should come after this WoD expansion. With no new places to go and no established-in-lore enemies left to fight, it doesn't matter how much more fun gameplay Blizzard can introduce. There's a limit to everything, and I think WoW will reach that limit in one or two more expansions. Even if consumer loyalty remains, creatively speaking, there's just not much more WoW can do than what it's already done. WoW should quit while it's ahead. Blizzard can always make a new MMO using some other theme/story once WoW is over.