XCOM Series.

The XCOM series is one of the great comeback stories of the strategy genre. Originally Published by Microprose, this sleeper hit was a hybrid Base management and turn based combat game on an isometric plane.

The Original Game was originally know as "X-COM" in the United States, and "UFO: Enemy Unknown" In its home country of England, and featured Pixel Graphics. One of the big features that really sold the player base was destructible terrain, and the soldiers that gained experience over time, adding minor RPG elements to the game and making the loss of an experienced soldier a crushing blow.

The original plot involved a secret Alien Invasion from Space, and the governments of the world coming together to form the X-COM project. The game involved shooting down flying saucers, shooting the aliens that survived so you could reverse engineer their gear, and finally taking the fight to the aliens on Mars where the final confontation involved dealing with an alien supercomputer.

X-COM is notorious among gamers for the RNG. Extremely unlikely misses seem far more common than expected, and the standard joke of "That's XCOM, Baby" when your soldier misses a point blank shot is legend.

This was followed by a sequel "X-COM: Terror From the Deep" in which everything was made considerably harder. It was primarily an asset swap with some new maps and tilesets.

The plot of this one was that the great ancient aliens that lay under the sea were awakened by the destruction of the Aliens from the first game, and now all of your weapons from the first game do not work and you're out of the alien material from the first game as well. Essentially this was a hand wave to put you exactly back in the same situation as the first game. Of course now, most of the game is set underwater, and you're stuck with crappy underwater weapons for most of the game. The final confrontation had you dealing with a great ancient sleeping alien in the ancient city of T'leth...

The Third Game in the Series was "X-COM: Apocalypse". This was when XCOM began to stray from its roots, introducing real time combat, Alien Allies, and Dimensional Travel, all set around one Fortress Megacity which was established to be the last human city after the world was poisoned in the last game. Interdimensional aliens who could strike anywhere was the big gimmick on this one, and while the game was successful, it didn't really move the series forward.

The fourth and Fifth games in the series were not Turn Based strategy games. "X-COM: Interceptor" was a space flight sim, ala Wing Commander, and "X-COM: Enforcer" was a 3rd person action game with one superhuman soldier, completely ignoring and inverting the plot of the previous games.

Many years went by, and "The Bureau: XCOM Declassified" was announced. This was a 3rd person Cover shooter, set in the 50s, using X-COM aliens. The fans were extremely disappointed by this game, because once again, it wasn't a turn based strategy game. Although it is suggested in later games that the events of this game (Involving ANOTHER alien invasion, but this one in the fifties and completely redacted by the US government) is what caused the actual formation of the X-COM project in the later Remake.

"X-COM: Enemy Unknown" Was a remake of the original game. We're completely back to the original plot of the aliens invading earth and being opposed by the government funded organization, X-COM. Gameplay was considerably speeded up, and cover became an essential tactical move. In addition, the character models were greatly improved. Voice acting for all units was added, and in general this was a remake that hit all of the right numbers. It was quickly followed by an expansion "X-COM: Enemy Within" Which added a Human Enemy faction of collaborators called "EXALT" as well as allowing your soldiers to become cyborgs or Genetically grafted superhumans with the expansion of the research tree into "Meld" technologies.

"X-COM 2" With X-COM being a notoriously hard game, especially at higher difficulty levels, the plot of XCOM 2 followed the most logical path. What if the Commander LOST the war? The assumption made in the sequel is that many of the characters from the first game were **** to go underground and form a resistance against the occupying aliens, who have now taken over the world in a "Benevolent" dictatorship. Thanks to their liberation of one alien vessel, they have a mobile command base, and travel the world trying to fight back against the aliens, and maybe free their planet. This Too was followed rapidly by an expansion called "X-COM 2: War Of the Chosen" which added 3 "Boss" enemies who would hunt X-COM mercilessly. Fortunately, the game also added three high powered "Resistance" factions as well as new areas and a heck of a lot of fun new weapons and units, including AI battle robots and Alien Defectors.