The Earth has been taken over. Worse, we surrendered it to alien forces. 20 years have passed since that surrender, and people are looking anywhere for hope of freedom. The only hope there is though is the scattered unit known as XCOM. In XCOM 2, the aliens rule Earth, and are trying to show that they "care", while also showing their true colors to those who dare defy them. 
As part of the remaining XCOM forces, you must rise up to save Earth from the occupation. You are outnumbered, you are outgunned, they are always hunting for you. But, if you're smart, and use strategy, you might just be able to finally take Earth back.
Through a new mobile command center you'll plan out your next strike. You'll now have options on where to go, who to fight, how to try and get support from the Earth's citizens, and when to try and stop enemy operations.
There are five classes you can make your soldiers. Build them into the ultimate team, then take them on missions that can change the fate of the world. Just know that the enemy won't make it easy.
XCOM 2 allows you total freedom in how you fight your enemies, including what skills and abilities your soldiers can learn. Make special areas on the Avenger so that your team can grow, get new weapons, and truly take the fight to the aliens. Be warned though, every mission is its own test, so you need to be ready for anything the aliens, and the world, may through at you. It's time to retake Earth, so suit up and go do it.