https://www.bungie.net/en/Explore/Detail/News/51030 or https://destiny.bungie.org/bwu/399

cheapLEY (and everyone else I guess)... er uh... TL;DR

Da da da da rehash of all this stuff

Legendary Campaign

It harder, and it will adjust per amount of folks are with you, but if you pull it off you get cool stuff like;

• We've got double chest rewards offering 1-3 extra chests per mission. Each chest will give you world pool gear, XP, upgrade modules, and Glimmer. ...
  
• A set of gear 20 above the soft cap at 1520 Power Level. ...
  
• Witch Queen Exotic armor that typically is reserved for PED Lost Sector drops. ...

...AND MORE!

Blah blah, more stuff about how this is going to be harder, but you don't need to read that stuff because YOU'RE A BAD ASS!

HOW HARD COULD IT BE?! LOL! (/s ...duh.)

...Then some marketing...

Exotics

There is more details about the stuff known, here is the stuff that wasn't;

The Loreley Splendor Helm for Titans is more than just a pretty face, it has the Cauterizing Flame perk that allows for Sunspots to heal players when they have Sun Warrior. Critically wounded? No big, the perk also ensures that a Sunspot is created in your location to give you that one last fighting chance with that quick grenade and melee ability recharge and longer Supers. Plus, more damage? Always a good thing.

...Renewal Grasps to look forward to with the Depths of Duskfield perk. This gives Guardians a much larger radius for their Duskfield grenades, while also nerfing incoming damage for allies within the Duskfield's range. Any targets locked within that space will also deal out a reduced amount of damage, so go out there and make those Hive cry.

And finally for this TL;DR...

The Witch Queen Release Schedule
To prepare for the launch of The Witch Queen on February 22, Destiny 2 will undergo scheduled downtime from 7:00 PM PST (0300 UTC) on February 21 to 9:00 AM PST (1700 UTC) on February 22. Below is the scheduled timeline for this release:

• February 21, 7 PM PST (0300 UTC): Destiny 2 is brought offline.
  
• February 21, 9 PM (0500 UTC): Pre-load for Hotfix 4.0.0.1 will be available on all platforms.
  
• February 22, 9 AM (1700 UTC): Destiny 2 will be brought back online. Hotfix 4.0.0.1 will be playable on all platforms and regions.
  
• February 22, 11 AM (1900 UTC): Destiny 2 maintenance is scheduled to complete.