-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.

If you just care about unlocking the ability to fly in the new expansion, and you should, the site’s Pathfinder tool is a must-bookmark. Its Character Planner is also incredibly useful for getting a sense of what you could (or should) do next, based on your recent activity, the gear you’re wearing (and would like to upgrade), achivements you’re close to unlocking, et cetera. If you want a simpler guide, the site also has a great list of all the activities you should be doing each day and week in Battle for Azeroth.

The Horde will now control most of Kalimdor, and the Alliance most of the Eastern Kingdoms. For a low-level character the quests and storylines won't change, but for high-level players many zones will see changes via phasing. Teldrassil is burned and Undercity is in ruins as the story progresses by phasing. At max level Arathi Highlands and Darkshore are phased to be updated to reflect their status as locations for Warfronts.
PLUNDER THE ISLANDS OF THE GREAT SEA – Explore Azeroth’s uncharted isles in Island Expeditions. Battle in groups of three as you race against cunning rival intruders (or enemy players) to collect the island’s resources and fuel the war effort. Constantly evolving challenges await as you traverse frozen landscapes near Northrend, open the gates of an abandoned Gilnean castle, navigate a war between elementals, and more.
The idea of the expansion came up after the heroes of Azeroth dealt with so much external threats like the Burning Legion. In their own words, "so when we talk about what's the biggest threat in this world, is it the titan or is it the dwarf paladin that put a hammer in that titan's head"? As such, the enemy (at least during the early parts of the scenario) will be the opposite faction, a "vast army of world-destroying forces".[4]
Island Expeditions are three-man scenarios that pit the team against three enemies using what Blizzard calls “advanced A.I.” That means the enemies will act more like players, pursuing goals proactively and filling class roles. The expeditions take inspiration from action RPGs, with randomized areas that mix up the experience each time. Players’ main goal will be obtaining resources more quickly than their foes, and expeditions should last 15 to 20 minutes. While primarily meant for PvE, there is a PvP mode that replaces the opposing A.I. with teams from the enemy faction.
Heirlooms: Heirlooms are the best source of bonus XP for leveling. All slots can be gotten pretty easily now, except the rings. The time you need to spend to get the rings if you haven’t gotten a level 3 shipyard in WoW is way too long, so getting the rings is generally not worth it. Having all your heirloom gear will boost XP by 55%. Generally, you want heirloom gear with crit on for leveling as you want to kill mobs in a few hits as possible
What’s worse, it’s rarely satisfying when you do make it to a new milestone in your grind to unlock the gear you need. Legion had legendary items that changed the way an ability functioned, which would also completely change the way classes played; the Azerite traits in the Battle for Azeroth are rarely as interesting. Instead, they are simply passive bonuses that, in most cases, help you do more damage without any extra effort on your part. While some classes are lucky enough to have traits that change their gameplay slightly, Blizzard has so far seemed to favor nerfing those traits out of viability for most specs.
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.