SINGAPORE — XCOM: Enemy Unknown was one of last year’s much lauded turn-based strategy games, and for fans who have sunk hours into taking down the alien menace there’s a new reason to revisit the game: The expansion, XCOM: Enemy Within is out tomorrow (Nov 15).

First timers also have a reason to get stuck on it, as the great gameplay returns with new tweaks that make things more compelling.

The basic story-line remains the same: Aliens are invading earth, and it’s up to XCOM, a top-secret organisation, to stop them. You take command of the XCOM base to conduct anti-alien research while also leading a squad of soldiers into combat missions.

One key difference in the expansion is the “enemy within”. EXALT, a human paramilitary group, has formed, and they aim to use alien technology for their own nefarious means. Left unchecked, EXALT will steal your money, slow down your research, or raise panic in countries. You can respond as and when this happens, but the real fun is in being proactive and setting up your own covert operations to track them down. Each cover operation requires you to send in one soldier armed solely with a pistol, and you will have to extract the soldier after a few days in-game. Be warned, not all soldiers will make it back alive even after a successful extraction.

Another big change is the introduction of MELD, which is used to implement genetic modifications or convert your soldiers into cybernetic soldiers known as MECs. Genetic modifications provide powers such as better eyesight, which is an added bonus over what’s in the game, but MECs provide something novel. For MECs, your soldiers become a walking tank, and it really allows for some serious destructive power if you can afford the upgrades.

The game does imply that both “advances” might be unethical — after all, for MECs, the solider ends up more robot than man — but while you might feel a slight revulsion at first it’s not too difficult to overcome that in the name of beating up ET.

The introduction of MELD also increases risk-taking and raises the pace of combat missions. If you do want to modify your soldiers, you’ll have to harvest MELD, which come with a countdown timer — take too many turns during combat to reach it and the MELD self-destructs. This makes battles more exciting than before, and is a welcome addition.

That’s not all, a new base defence mission has you defending your base against an alien invasion with a thinned-down, mostly untrained crew. Sadly, it only happens once a game — it’s a rather thrilling situation that’s worth revisiting. For seasoned XCOM gamers, there’s also many new maps, including a rather impressive dam, to keep things fresh.

None of these really change the game much, but the additional variety really helps stop you from feeling like you’re visiting the same city again and again.

With all these new additions it is easy to think that the expansion has made the game more confusing or less focused, but that’s not the case — the additional changes help ramp up the challenge, and the end of the world has never felt more dire. XCOM: Enemy Within is a worthy addition to the XCOM series, and bodes well for the inevitable sequel.

Rating: 4/5

Platforms: PC (S$39.90), PS3 (S$49.90), and Xbox360 (S$49.90)

Release date: Nov 15, 2013