XCOM: Enemy Within Previews

Firaxis' Enemy Within expansion pack for XCOM: Enemy Unknown is the subject of two new previews, including a relatively short piece on Electronic Theatre...
The Mec Trooper is a hefty beast capable of absorbing great amounts of damage; so much so in fact that it actually has an ability that allows it to become temporary cover for other units. When in the attack it's not exactly a light weight, with the Collateral Damage ability able to destroy cover and damage any enemies behind it even at a distance while the Kinetic Strike presents a rocket powered fist that dishes out up to twelve damage points to anything it strikes up close. Of course the greys have their own version of the Mec Trooper to keep things balanced, so players will have to learn the best tactics to overcome this great strength.

A second new addition to the troop types is that of the Gene Mod soldiers. These are renovated versions of regular troops which have greater specialisation but are no stronger than regular troops. This specialisation, as you might expect, is directly Electronic Theatre Imagerelated to their class giving them a significant advantage, such as snipers being able to mount high lookout points for greater range and accuracy.

...and a slightly lengthier one on GameGrin:
Another way in which the maps are changing is the introduction of Meld, a new collectable resource which appears on the map during any mission. Meld is used to unlock new soldier abilities and research options and will prove invaluable to advancing the XCOM cause. Meld will be placed on the new maps, and integrated into old maps, and must be captured within a limited amount of turns to be utilised. This time limit changes the dynamic of play by forcing the player to choose between slow and safe gameplay, or taking a risk based on the promise of potential reward.

Our time with the game really served to demonstrate how the introduction of these new features creates a very different tactical experience than in the core game. Our mission was a UFO crash site in a farm location, in which a mix of regular, genetically modified and MEC troopers faced a powerful alien force, including a number of Mectoids.