XCOM 2: War of the Chosen is the first major expansion for the tough-as-nails turn-based strategy'er XCOM 2 [GN score: 8.8 out of 10]. It arrives next month. It's been less than a year since I've touched XCOM 2, but I know I need to brush up on my skills.
War of the Chosen adds a frightening cast of ADVENT enemies, the Chosen, who are three inter-warring (or at least argumentative) alien leaders. Plus, War of the Chosen introduces three new potential allies; they're three resistance groups that are all fighting among each other, too. Everybody's already locked in a pseudo civil war. I'm guessing you, Commander, will want to unite the good guy side before the bad guys unite their side.
Because the Chosen are coming after you specifically, Commander. Just as you had been captured between XCOM: Enemy Unknown and XCOM 2, the Chosen want to put you back on ice. Cut off the head and the body will flounder, as they say.
On the Chosen side we have the Assassin, Warlock, and the Hunter. (I expect a video for the Hunter will arrive shortly from Firaxis.) They lead a new pack of enemy units: psionically charged Priests, explosive Purifiers, and sneaky Spectres.
The Lost are a fourth enemy, appearing to be a zombified mob, roaming in packs, attracted to the sounds of battle, and leaping out of the fog of war by the dozen. Not sure if they're on anybody's side, but I'm pretty sure they're not doing you any favors on the battlefield.
On XCOM's side, we've got the Reapers, Skirmishers, and Templars. I'm not gonna lie: It looks like Firaxis took several pages out of Bungie's art studio and made these new units look like Destiny character classes. There are worse inspirations they could've drawn from, though. Reapers are explosive snipers. Skirmishers have a nasty, neato, multi-tool grapple. Templars have psionic power well beyond XCOM's.
You want all of these guys on your side, because there's no way you'd want to face these guys fighting against you.
XCOM 2: War of the Chosen launches on PC, PS4, and Xbox One on August 29.