Eventually, the Alliance finishes its preparations and launches an attack on the Zadalari capital of Dazar'zalor, their goal being to sever the budding alliance between the Zandalari and the Horde by dismantling the Golden Fleet and capturing King Rastakhan. Despite Anduin and Jaina's desire to capture him alive, Rastakhan is overwhelmed by the power of his pact with the Loa Bwonsamdi, and the Alliance champions are forced to slay him. Enraged by Rastakhan's death, Horde champions launch a vicious counterattack on the withdrawing Alliance forces, which ends with both Jaina and High Tinkerer Mettatorque gravely wounded. As the Alliance leadership debates their next move, Sylvanas, infuriated by the Horde's defeat, resurrects Jaina's long dead brother Derek Proudmoore as a Forsaken, an act that horrifies the surviving Horde leaders, with the intent to use him as a sleeper agent to destroy the Proudmoore family from within.
-PvP- Completely broken for some classes and I mean broken going from both sides of the spectrum, from classes destroying everyone, to classes that can't even kill another player. It's fairly common for a weak class to lose to a powerful class even if the weak class outgears them by 50+ ilvls. That's how broken PvP is and Blizzard doesn't seem to know what to do to fix it other than do blanket damage nerfs/buffs as those are the only changes we've seen.
XP Potions: The Elixir of Rapid Mind and Elixir of Ancient Knowledge no longer drop. They can be bought on the AH still but are way to expensive for it to be worth it. The Excess Potion of Accelerated learning is available from your garrison quartermaster but only works for level 91 to 99. As of Patch 8.1 you can also buy the 10% XP Potion Draught of Ten Lands.
We’re also big fans of Simple Armory, which gives you a similar look at your overall progression acrosss the entire game, as well as a gorgeous, detailed graphical listing of all the achievements you’ve unlocked and all the mounts, companions, pets, and toys you’ve collected. The site makes it incredibly easy to see what you still have to get, if you’re a completionist. If you’re looking to fill out your collection of mounts, the site will even create a handy, optimized guide of how you should spend your day (or week) adventuring to acquire them all.
For Alliance it's Lok'Modan, Redridge, Darkshore, Felwood, Stranglethorn (both parts), Plaguelands. Somewhere between 3 - 3.5 of these get you to 60 in like a 16 hours /played, if you queue for dungeons at the same time. I recommend dropping everything at 45 and going to Darkshore-Felwood if you didn't do them yet - they are literally the fastest levelling zones in the game right now, maybe only trumped by Silverpine.
-Gameplay- Gameplay has largely been stripped down to be a shell of its former self. This trimming has been going on for several expansions, but now it's even worse. Classes only have so many buttons which has resulted in very little skill involved in PvE (even PvP is a faceroll for most melee, lacking any sort of depth and decision-making as it's pretty clear what buttons to press in any given situation) and it's become more of a gear check. This expansion gave zero new abilities to classes, only took them away.
At 98 you have the option to drop what you're doing and return to your capitol city to start the quest for your Legion Artifact weapon. However, I do not believe this is necessary to do right away unless you're struggling with kill speed in your current gear. I would recommend waiting for a natural pause, such as hearthing to repair and clear your bags. From 100 to 107 you won't even really fight mobs that often; only just enough to clear the way to any treasure you need to pick up.
If you love running old content for transmog items, you'll love the new legacy loot system. Whenever a player enters a dungeon or raid where they are 10 or more levels above the content, the dungeon or raid bosses drop an amount of loot equivalent to what would have dropped for a full group when the content was current. That means players could earn loot for five people in dungeons and loot for 20 people after soloing a raid. The legacy loot system also drops other gear types, like cloth dropping for a plate wearer. It's now much easier to get the transmog gear you want, and you can also collect gear for your alts on the same run.