Following players' feedback on Enemy Unknown, Firaxis added procedural generation of maps and mod support to the game.

The developers set the game after the bad ending of the 2012 reboot because it allowed them to change gameplay, introduce various new features and redesign some enemies.

The game was also praised for its difficulty and the addition of modding tools; criticism was mainly directed at its poor performance at launch.

Played from a top-down perspective, the game uses turn-based tactics in which players issue commands to a squad of human soldiers to eliminate the aliens in a map and dependent on missions, complete secondary objectives.

Enemies will attempt to flank and exposed soldiers will sustain heavy injuries from attacks due to the lack of any defense.

[14] The game has five character classes, each with its own Soldier Ability: Ranger wields a melee weapon that slashes enemies, Grenadier has a grenade launcher and explosives that can destroy enemy cover, Specialist has a drone that improves the team's defense and health, Sharpshooter is the team's sniper, and Psi Operative—which is unlocked late in the game—[15] uses telepathic and psionic powers.

[14] If the soldiers survive and complete the mission, they gain experience[19] and will be promoted, unlocking new options in the skill trees and customization items.

The Armory[3] allows players to recruit soldiers and customize their personalities, names, costumes, genders, nationalities, and weapons.

[25] As the game progresses, new facilities that allow players to increase squad size, improve combat performance, and craft experimental weapons are unlocked.

[25] At the bridge of the Avenger, players can access the Geoscape, advance time, move the Avenger, access scanning missions and combat missions, visit the Resistance HQ to purchase new engineers, weapons, and soldiers, trade with the black market, and discover supply caches and bonus equipment.

The game begins with Bradford leading a raid on an ADVENT building to rescue the Commander, who had been captured and put into stasis.

Tygan tells the Commander that while they were in stasis, ADVENT used their brain to gain tactical data and facilitate the conquering of Earth.

The Spokesman orders the Commander to unite the resistance groups around the world and to discover the true nature of ADVENT's top-secret Avatar Project.

The Spokesman is presumed killed when he sacrifices himself to warn XCOM about the plan, ordering them to hijack ADVENT's global communication network before they can make the announcement.

XCOM hacks the network and transmits proof of ADVENT's crimes to the world, causing a global revolution against the alien occupation.

People abandon ADVENT's cities to join the Resistance en masse, and the military remnants are ineffective without their leadership.

Nonetheless, the developers drew on elements from the original games, including procedural generation and gameplay unpredictability, to XCOM 2.

[32] The team found the new setting is thematically suitable for the squad-based gameplay and that it enabled them to create new alien designs and reset the research options.

[31] Environment storytelling is an important part of the game; for instance, in the megacity there are signs indicating ADVENT has taken over the world whereas other maps and areas show players the remnants of human civilizations.

[36] The gameplay was initially designed to be forgiving but after receiving feedback from play-testers, who noted the game was too simple and that a lot of systems failed to engage players, the idea was scrapped during the late stage of development.

Therefore, the team added valuable loot drops, time-sensitive objectives, and the idea of "concealment", in which recruits can ambush the aliens, forcing players to take more risks during gameplay.

For instance, completing a side-mission that nets players additional resources may mean the aliens may have made further progress with their Avatar Program.

[43] Classic XCOM enemy Sectoids received a new design, which looks "more feral, more imposing" after the species blended with human DNA.

[50] Players who ordered the game before release received a new recruit and the Resistance Warrior Pack, which has extra customization options.

2K collaborated with video game collectible maker Project TriForce to create a Beam Pistol replica for players to purchase,[51] and partnered with novelist Gregory Keyes, who wrote a prequel novel named XCOM 2: Resurrection that was released on November 10, 2015.

[54] Gamepad support for PC and a mode that allows players to explore the Avengers headquarters in first-person perspective were released in November 2016.

[71][72][73] Nic Rowen from Destructoid praised the game for building on the original and expanding the number of tactical options offered to players.

[86] Writing for Polygon, Charlie Hall stated that he enjoyed the concealment system, which he felt that successfully adds new variations to the XCOM formula.

[86] Tom Senior from PC Gamer called the experience "gripping" and added that "the game cleverly uses scarcity of opportunity to force you into difficult dilemmas".

Stanton and Stapleton praised the game's artificial intelligence, which would take every tactical advantage it has to put pressure on players.