At 96 the standard wisdom is to immediately drop what you're doing and proceed to Spires of Arak and do the quests to unlock the Inn, granting a further 20% experience bonus while in that zone. You'll want to do that eventually anyway, but I'm not sure it outweighs the quest experience from Gorgrond. However, if you decided to go to Spires immediately at 96, restrict yourself only to bonus objectives and again leave Treasures until you're 100+. Make certain that when you being the quests to unlock the inn, you speak with the quest NPC to also learn Archaeology, since it's required to collect several of the treasures in Spires.
The expansion is set immediately after the events of Legion. Two continents have been added within the Great Sea between the Eastern Kingdoms and Kalimdor: Kul Tiras, one of the major human kingdoms, and Zandalar, the homeland of Azeroth's trolls. While the Alliance and Horde will initially travel to one continent respectively, both continents will be available to both factions at level 120.
-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.
As for the classes themselves, they almost all play like slower and slightly less interesting versions of their Legion counterparts. This is thanks in large part to the loss of one ability from each class that came along with Legion’s own AP dumping system: the artifact weapon, which added a unique ability to every spec in the game. The loss of these abilities left most classes feeling frustrating and incomplete, and though Azerite gear was supposed to be the replacement, it missed the mark completely. There will always be one Azerite trait that reigns supreme for each spec, meaning that the frustration of that particular loop will be unavoidable as long as the system is in the game.
There are also a number of different online tools you can use to make yourself a better World of Warcraft player—and to help you decide what to focus on. Wowhead has a great Attunement Tool that shows you how close you are to unlocking significant milestones in the game, like unlocking new allied races, earning reputations with key factions (which will ultimately help you unlock faster mount speed and other goodies in the game’s expansion), and how far along you are in your dungeons and raids.
I do not recommend going for TBC, although I remember Hellfire peninsula to be decent, everything else is rather slow. Instead go for WotLK, Borean Thundra gets you levelled very fast, and then you can head straight for Icecrown at 67, which is also insanely fast, although admittedly has a few elite quests. You can go to Sholazar Basin alternatively. 2 zones should get you 60-80 no problem.
For Horde, Vol’Dun the area captures the feel of Battle for Azeroth is both the hardest and continues than other areas in the game. It can get quite frustrating in this area so better to go it early when you can utilize your old gear. The next two areas are highly dependent on personal opinion – Nazmir is filled with mobs and Zaldalar is one of the easiest zones.
Kul Tiran human (8.1.5) - "Kul Tiras was founded by fearless explorers who sailed uncharted waters in search of adventure. As a key member of the Alliance of Lordaeron, the Kul Tiran navy dominated the seas of Azeroth with its legendary fleet. But after years of turmoil and hardship, the kingdom grew isolated and vulnerable to dark influences. Thanks to the help of brave heroes, House Proudmoore has been restored and Kul Tiras is poised to fight alongside the valiant Alliance once more."
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.