War of the Chosen is a full scale expansion of Xcom 2 coming August 29th.
Read details of the expansion from the Creative Director Jack Solomon on ign
A summary of the new features from the expansion (from reditt)
-Rulers are now facilities guards and they will trigger in every mission like they used to be only after being engaged once. Rulers and Chosen can't be in the same mission.
-Chosen: the hunter snipes you from out of sight, it's avoidable by movement tho. The warlock summons ghosts. The assassin teleport into soldiers to melee swings.
-The chosen have a resource called "knowledge" and they can increase it by interrogating xcom soldiers, after they have enough knowledge they can reach your base. They can also capture your soldiers and you may need to rescue them in a stealth mission.
-They can screw you up in the strategic layer too and there is also a new base defense mission involving the chosen attacking the avenger.
-Every chosen is independent and they have their own knowledge bars and they control different territories.
-Every chosen has a stronghold in which you have to go in to defeat them permanently (think like EU alien base missions).
-The chosen gain new procedural perks and abilities over time. Nemesis system from Mordor ispired Firaxis.
-Little fun details added like factions or alien speaker radio transmission about world events while in geoscape, just to add flavor
-You are not obliged to beat all chosen before beating the game, but the chosen u didn't kill will show up all at once for a final confrontation.
-Different ending cinematic
-New enemies: Priest, mind control, revive himself, and many buffs. Purifier, flamethrower and incendiary grenades. Spectre, who knockout you soldiers and create an active copy of them.
-The zombies are a lot and come in swarms, but if you kill one straight you have a free action, basically you can chain kill them.
-New mission system in tactical: lot of missions have random modifiers, example: lot of explosives in the map\you can bring only 3 soldiers\free conceleament skill for all soldiers\etc. etc
-You can have more heroes but after the first they will be very hard to get
-2 new facilities: training center, for new abilites for soldiers and Resistance ring, related to covert ops
-Covert ops in which you send ppl out looking for intelligence but they can trigger missions in which you need to rescue them
-Bonds between soldiers work in both strategical and tactical by adding new stuff, like if one close to other is immune to mental effects and so.
-New fatigue system
-If u bring fatigued soldiers in missions they may panic, or do bad stuff like reacing badly to many events so it's doable but very risky
-New item: Lost lure, who can make zombies attack where you want
-Every faction and chosen has new weapons you can get , so basically 6 new weapons.
-New research stuff called Breakthrough or Ispiration, they appear randomly and allow many buffs like increase sniper rifle damage or decrease a facility cost
-Improvements fixes on engine, such loading times and framerate