Scaling Zones
Shortly after you enter the Broken Isles (Legion's new continent), you'll be asked to choose your starting zone. Unlike previous expansions, zone order doesn't matter because enemies now scale to whatever level you are. Certain enemies in the world also scale their hit points to the number of characters fighting it, ensuring fights can't be cheesed by a high level player.
Artifact Weapons
There are no weapon drops in Legion zones or dungeons. Early on, you will acquire a powerful Artifact weapon, which is tailored to your specialization and levels up independently of your character.
Earning your Artifact weapon involves a short, single-player story quest that will ask you to master the particulars of your spec. As an Outlaw Rogue, I was tasked with sneaking through a mine-littered beach, capturing a pirate ship, and solving several combat puzzles that require skills only my spec contained. These quests are well-designed and do a lot for making you feel like your class actually has a place in the world outside of their combat role. I've done four of them at this point, and I'd love to eventually do them all.
Artifact weapons start with one ability that you can add to your hotbar, and as you level it up, you'll be able to add points to its talent tree and gradually unlock more power. Your Artifact also has three slots to socket Relics, which grant bonus points in its talent tree and boost its item level. Higher item level means the base stats of the weapon scale up. This is a great alternative to how similar weapons are earned in other MMOs (I'm looking straight at you, FFXIV's Anima Weapons).
After you get to level 102, you'll be presented with the option to hunt down the other Artifacts available for your class, so don't worry on missing out!
Class Campaign & Halls
This is one of my favorite new additions to Legion. Once you reach Dalaran in the expansion, you'll be contacted by a representative of your particular class, who directs you to your Order Hall. As a Rogue, I was introduced to The Uncrowned, who occupy the Hall of Shadows, hidden underneath Dalaran.
You'll be sent on missions to advance an agenda for your class that ties into the overall Legion storyline, acquire your Artifact Weapons, and eventually recruit champions to your cause. Champions can accompany you in battle, or be sent out on missions, similar to how Garrisons worked...
...except this time, Blizzard wisely released a smartphone app that allows you to handle all of that stuff without being logged into the game.