My mistake was to assume mechs wouldn’t explode. I had one soldier sat up on the back of a parked pickup truck, another in cover behind a tractor, both taking pot-shots at a sectoid’s mech (yes, they’re called mechtoids). I’d moved my own mech in close to deliver a killing blow with its powerfist. Things didn’t go exactly to plan. The alien exosuit exploded, then my mech exploded, then the truck next to the mechs exploded. Everything exploded.

XCOM: Enemy Within: still XCOM.

Enemy Within is interesting. It’s a meaty expansion that adds masses of new maps, the chance to genetically alter your troops, and mechs. It’s not a brand new story: it’s a combination of new options that fill out the middle and end game. Think of it as XCOM’s equivalent of a Civilization expansion: new tactics, opportunities and threats. It’s an invitation to replay XCOM.

And who wouldn’t want to replay XCOM?

At Gamescom, the XCOM team were showing off part of what’s new: the chance to genetically modify your soldiers, new Mech units, and new tactical levels – here a cluttered, rundown farm that wouldn’t look out of place in the Texas Chainsaw Massacre. To the North was a downed saucer. Between my men, and the prize, a farm’s worth of farming detritus and aliens. Aliens everywhere.

Even if XCOM isn’t a new story, when you play XCOM with Enemy Within installed the game will prioritise the new maps. “When you start a new game of Enemy Within you’re very, very likely to see the new maps that you haven’t seen yet first,” says Producer Garth DeAngelis. Apparently, Enemy Within’s new maps expand the game by almost 50%.

Thankfully, I wasn’t charged with leading a group of green recruits against the menace. I was leading a squad of genetically engineered super-soldiers, partied with a pair of mechs. My sniper had a pair of spring enhanced legs: able to leap onto the roof of a nearby building before entering overwatch. A soldier had the brainiac brilliance of a Sectoid Commander: able to repel and respond to psionic attacks with similarly powerful brain rays. And my mechs: ooh, they’re lovely things, hulking armour plated beasts with miniguns for arms.

All told, with this level of firepower, and a medic, it should have been an easy win.

XCOM: still a game where overconfidence is your biggest enemy.

These new toys will be the death of you.

My joy at seeing my sniper jack-in-the-box bounce on top of a nearby shack was shortlived: he died the very next turn at the hands of a group of Sectoids he’d exposed himself to.

Seeing a canister of Meld, a new resource that allows you to purchase genetic and mechetic material, I dashed my soldier over to a pick-up truck. Meld canisters will self destruct if not retrieved quickly: it’s a mechanic that Firaxis believe will draw cautious players into being more aggressive.

But in the process I revealed a Mechtoid: a sectoid Mech with just under a trillion hitpoints and a plasma cannon for an arm. It ended in explosions.

Which left me with one mech and a wounded medic. You’d expect that this would be my trigger to start playing a little more cautiously.

Except, it was a lot of fun punching that mechtoid. I mean, a lot of fun.

My new plan: punch everything.

When you punch an alien with a mech it doesn’t just stand there. It’s body becomes a projectile. If aliens hit cars, they’ll cause an explosion. Aliens can smash through cover. Or even more.

“Something that didn’t come out in the demo with the kinetic strike module was that you can actually punch an enemy through a wall,” senior game designer Anand Gupta told me. “As in, the enemy’s on the other side of the wall and you can punch through and strike them. And you might ask “How can I see there’s an enemy on the other side of the wall?” but if there’s a genetically modified soldier nearby with bioelectric skin and you can see his energy field.”

I can’t wait to use that against Jeremy in our next multiplayer battle.

There’s obviously more coming: beyond mechanical changes, in an effort to make your team sound more international, Firaxis have included “all the voice data so that all the soldiers have access to all the localised languages,” Gupta said. “It’s obviously a much more comprehensive and customisable way of getting the soldiers to not sound American in this international organisation banding together to fight aliens.” Having soldiers shout to each other in different languages as they leap crates and shoot sectoids is surprisingly effective.

I loved my time with Enemy Within, yet, I’m quietly quivering about what Firaxis aren’t showing.

For a start, Gupta and DeAngelis were only willing to talk about the new features that had been added to XCOM’s tactical layer: the genetic modifications, meld, new maps, and the mechs. When I tried to draw them on changes to the strategic layer all Gupta would say was that “one of things with XCOM that fans really like is that it’s a strategy and tactical game, they feed each other. Most of all you’ve seen is tactical but there’s no question that we would not be doing justice to what people like about XCOM if we were only to expand the tactical. Rest assured that there are substantial expansions to the strategy layer.”

Gupta and DeAngelis excitedly told me they’d be speaking about the rest of the expansion “soon”.