Enemy Within's single-player campaign starts the same way as Enemy Unknown -- bunkered in an underground military base at the brink of the end of the world, following the escalating war with the aliens to its climax. Think of the expansion as a lateral addition to a core game and mission list that remains unchanged. It's possible to play Enemy Within almost exactly like Enemy Unknown, but Enemy Within adds an optional quest line early on: Defend the XCOM nations and XCOM itself from a transhuman threat... an organization called Exalt.
To further humanity's evolution, Exalt attempts to disrupt XCOM operations and promote the assimilation of alien technology into human biology. Thick with narrative irony, XCOM simultaneously develops two tracks of transhuman upgrades, the exact kind of alien-human integration that Exalt wants: MECs and gene mods. Each unlocks after the construction of cybernetics or genetics labs, respectively, enabling the manufacture of XCOM super soldiers to combat both Exalt and the Sectoids' breed of elite soldiers. The new soldier buffs come in two forms: the first is a hulking Mechanized Exoskeleton Cybersuit (MEC) with crushing weapon attachments. The second is through stat-boosting genetic modifications. Both are governed by an alien resource called Meld, which now litters each map in glowing orange canisters. Harvesting Meld is as easy as positioning a troop next to a canister, but it adds another objective to each map, and a countdown timer for each maintains the tension that underpins the XCOM series. I made more than few foolish dashes to gather Meld that evolved my tactical approach from cautious advancement to frantic survival when suddenly ambushed.
For the first ten or so hours, Meld abounds and players are free to explore the potential of MECs and gene mods. To balance this advance, dedicating a soldier to one excludes him or her from the other. MECs lose their class-specific abilities, beef up on armor, and gain the potential use of flamethrowers, kinetic strikes, healing spray, grenade launchers, proximity mines and electric fields. Their robotic metal shells can also serve as cover or bullet sponges, opening up opportunities for some devastating close-quarter attacks.
Thankfully, it's not always enough. The design temptation here might be to add content and then just turn players loose. Firaxis resists, and complicates each level with advanced enemy units and cleverly placed enemy spawns. I say "cleverly placed" in hindsight; at the time, a rush of three Chrysalids could not have been more terrifying, especially on Classic difficulty, without auto-save. Note that multiple auto-saves are disabled by default on Normal. Classic and Ironman continue to be brutal tests of willpower and patience. You've been warned.
Just as Meld upgrades the XCOM soldiers, it's also responsible for a host of new enemy units. The Mechtoid, a Sectoid mounted in an oversized metal rig sporting two piercing plasma rifles for arms, parallels the human MEC in size, health, and damage dealt. Meld-enhanced Exalt agents have access to the same buffs as gene-modded soldiers. And the Seeker, a floating, tentacled stealth squid, cloaks and face hugs to take soldiers out of action. A few late-game surprises also dial up the challenge, particularly in Council Missions and Exalt Covert Extracts.
If all this permadeath sounds like a bit too much, rest assured that there's always Normal difficulty and the option to reload auto-saves. If, however, you balk in the face of unidentified flying Armageddon, Enemy Within offers the chance to mix up play variables with new Second Wave options like Save Scum, which reseeds the random number generator that determines how percentage shots are executed, allowing players to play from the same save until the shot lands. Itchy Trigger Tentacle causes some aliens to open fire automatically on sight, leading to sneakier tactical play. Add 47 new maps to that permutation and your roads to death grow exponentially in number.
In response to claims of unbalance or inefficiency in the single player campaign, Firaxis has also tweaked some of the interfaces and abilities for the soldiers. New items like Reaper Rounds and the Gas Grenade make full use of the dual item slot upgrade from Officer Training School, while a much-needed "Make Items Available" button streamlines the process of equipping items to the rotating roster of healthy soldiers. In Enemy Unknown, to ready a fresh squad for battle, players would have to navigate to the item inventory for each out-of-action soldier, release the item, weapon, or armor, and then manually assign that to the new units. The "Make Items Available" frees up any items not being used by active squad members during preparation, turning a tedious task into a simple and efficient one.
The gamble here rests less on in-match strategy and more on complementary loadouts, to its credit and discredit. Credit is due for the revived multiplayer mode's turning focus towards the tactical mind game during battle preparation. You could find yourself nervously hoping that the enemy forgets to equip snipers with respirators and their MEC with jet-boosting boots so your Seekers can take out their roof support without interference from the MEC, then move in your plasma-wielding sniper to finish the job. The addition of Seekers does, however, present the opportunity for some world-class griefing, like if a team of all Seekers strangles every enemy unit simultaneously, ending the match. You can counter that kind of tactic, but only if you've spent the resources on respirators or bio-electric stealth detection or battle scanners. The fight in multiplayer has clearly moved to the shadows; a challenge that requires some thoughtful planning and a little paranoia to conquer.
Enemy Within makes even clearer the goal set out by Firaxis in Enemy Unknown: to use consequence as a means of creating value for player agency. Choices matter, but they matter even more when the stakes are higher. With 30+ hours of your time resting on your mortal soldiers' melded bodies, you're only ever one misfortune away from an expensive checkmate.
This review is based on a Steam download of "XCOM: Enemy Unknown", provided by 2K Games.
Dan Crabtree is a freelance game critic from the war-torn province of Northern Virginia. During times of post-Hellenic peace, he works as an I.T. guy and hangs with his dog, whom most consider handsome and well-read. He can be found on Twitter @@DanRCrabtree.
Note: Joystiq does not provide star ratings for downloadable content reviews with the understanding that the quality of the core game's experience is unchanged from the retail release; See our XCOM: Enemy Unknown review.