I've never been much of a fan of extra downloadable content packs in videogames.

Usually, when I finish a game's main storyline, that's it. The plot is over, I've saved the world, I've stopped the terrorists, I've rescued the princess, I've slayed the dragon. Done. But then comes DLC, or expansion packs, whatever you want to call it — little downloadable bits meant to extend the life of a game. Sometimes it's something as small as a new weapon or ability pack, sometimes it's a few hours of side story.

Generally, I've often found the experience to be something like watching the deleted scenes of a movie just after the credits roll. Sure, it's cool to see a bit more content, but having just finished the whole thing, did seeing that scene really enhance the experience all that much?

XCOM: Enemy Within, which will launch on November 12 for PlayStation 3, Xbox 360 and PC, is not that kind of expansion pack. Enemy Unknown is a fantastic game and highly replayable to begin with, but even so, I haven't touched it since completing my first playthrough. Enemy Within changed that.

Enemy Within is, at its core, the same game as Enemy Unknown. You still build an alien containment facility, capture and interrogate an invader, assault the alien base, etc. Almost every aspect of Enemy Unknown, from the cutscenes to the plot line to the missions, weapons, abilities, and maps are present — the expansion just adds more. Think of Enemy Within as a backpack full of goodies that you strap on to your favorite action figure that completely changes the way you play with it.

New maps add variety to the missions you undertake. New alien classes give the invaders a crop of new combat strategies to which you must adapt. Not only that, there's a new enemy faction: EXALT, a group of fanatic humans who view the alien invasion as a chance to further their hyper-futurist agenda. Their goal is advancing and enhancing the human race through alien technology — much like your team at XCOM — but rather than using it to defend the Earth's borders, they wish to seize power themselves.

The new MEC Trooper class offers powerful new options on the battlefield. Screengrab: WIRED

During the game, EXALT will sporadically sabotage the XCOM project, but in doing so leave one of their terrorist cell's locations exposed. You then can send a covert operative to disrupt their actions, resulting in a new type of extraction mission where your standard six-man squad must protect the under-equipped operative while he or she completes a series of objectives. The missions are exciting and fun and, since EXALT uses strategies more suited to their human physiology, offer a welcome change of pace from the unrelenting extraterrestrial force.

But the biggest thing Enemy Within brings to XCOM is the addition of Meld, a new collectible resource which allows for biological and mechanical enhancements to your soldiers. The former takes the form of genetic modifications — a new series of "this or that" powers that are available to all soldier classes. For example, you might be asked to choose from a leg modification that grants exceptional jumping power or adaptive bone marrow that speeds up recovery time.

The bonuses are cool, and let you further customize your soldiers to fit both their class roles and your personal play style. Even cooler, though, are the mechanical enhancements.

On the engineering side of things, Meld lets you turn any of your soldiers into the new MEC Trooper class, which forgoes gene mods in exchange for the ability to equip a powerful mechanical exoskeleton. MEC Troopers have their own tree of class skills, many of which focus on taking down groups of enemies or destroying cover, and are further customizable based on the abilities chosen on the exoskeleton and their class before becoming mechanical.

With the new class and abilities, I completely rethought how I approached combat encounters. My standard squad, their weapon and equipment loadouts, even their placement on the battlefield — it all changed, making my experience effectively replaying Enemy Unknown feel entirely new.