An extended campaign requiring far more missions to complete
Tactical missions that allow up to twelve XCom soldiers per mission with the right upgrades
Eight soldier classes: Infantry, Assault, Sniper, Scout, Gunner, Rocketeer, Medic and Engineer, and eight MEC classes: Valkyrie, Marauder, Jaeger, Pathfinder, Goliath, Archer, Guardian and Shogun
English-accent voicepacks for soldiers from England, Australia and several other nations
New and modified perks, including Ranger, Sapper, HEAT Warheads, Lock N' Load, Fire in the Hole, Hit and Run, and Javelin Rockets
New and modified technologies, including Xenopsionics, Alien Biocybernetics, Pulse Lasers, Gauss Weapons and Advanced Aerospace Concepts, and many new foundry projects
Five tiers of XCOM weaponry, many new armors and small items and S.H.I.V.s that can be equipped with perk-granting small items! See some of the new weapons here.
Earlier access to psionics and an expanded psionics tree
A system of commissioning and promoting XCOM officers who provide bonuses to your entire squad during missions (replaces the Enemy Within medals system)
Overhauled interception game, with five new UFO classes such as the Fighter, Raider and Harvester, as well as six interceptors per continent, foundry projects to upgrade your aircraft, individualized pilot names and pilot experience, and the Stingray Missile weapon system
Overhauled strategy game, in which the aliens gather resources and conduct research -- efforts XCOM must interdict if it hopes to save humanity. XCOM can now retake countries by finding and conquering alien bases in those countries. Help council countries defend themselves by fulfilling their requests for alien technology!
Aliens and EXALT forces grow tougher over time, gaining stats and perks
New weapons for XCOM soldiers
Soldiers rest after each mission, requiring the player to build a much deeper roster of soldiers
Modified Second Wave options to support longer campaigns
Most of the specific changes will be detailed in in-game text. Many game mechanics have changed, so read perk, tech and item descriptions closely! They may not do what you expect from vanilla.
