XCOM: Enemy Unknown is a bit like a sci-fi version of The Apprentice.

Plucked out of nowhere, presumably on the back of a dodgy, cliché-riddled CV, you are given a project to lead which involves strategy, research, diplomacy, finances, resource management and plenty of tactical battles.

If you are successful in each round you will keep your overlord happy and get to lead your team further into the process.

Of course where it differs from The Apprentice is the prize, with the stakes being very much higher. Rather than £250,000 of investment from Lord Sugar being up for grabs, it’s the glory of saving the planet from a hostile alien invasion that’s on offer. And if you fail it’s not just a swift exit from the boardroom you’ll face, but the end of mankind.

In XCOM: Enemy Unknown you play the unseen commander of the multinational XCOM paramilitary organisation tasked with defending the Earth from the near-future attack.

It quickly establishes itself as a game of two halves, both of them equally deep and absorbing.

You'll spend around 50 per cent of the time on isometric 3D battlegrounds around the world carrying out missions involving such things as eliminating specific alien threats, evacuating civilians, rescuing VIPs and investigating crash sites. Maps include cities full of cars and buildings, rural wooded areas and enemy ships.

The action plays out as tactical turn-based combat during which you control the individual movements of between four and six soldiers you've selected from your roster. Units come from various classes such as sniper, assault, heavy and support. They can be given different loadouts of numerous weapons and equipment, and also gain new abilities as they survive missions.

Each squad member gets two moves per turn which can include dashing into cover, shooting at an enemy or launching a rocket. A fog of war ensures you can only see the parts of the map your troops can.

Once you've made all your moves the enemy AI has its turn and the battle rages on until either your team is defeated or you've completed the several objectives attached to each mission.

Your Local Guardian: XCOM Enemy Unknown

Enemy AI is smart and mistakes during battle are heavily punished. If you leave someone exposed out of cover or if you get outmanoeuvred by a group of the aliens you'll be in all sorts of trouble.

Death is permanent so a fatally wounded fighter is out the game for good. I wouldn’t say characters have personality as such but they’re certainly not just faceless units so I’ve had little pangs of emotion when I’ve left some of my best men and women after getting familiar with them individually over the course of many missions. Of course, the real kicker when someone is killed is losing the valuable skills they’ve acquired.

Battles are always tense, dramatic and unpredictable – and I’ve found there is usually at least one memorable moment in each, such as a terrible error causing one of my best performers to perish, a spectacular kill or a last-gasp move that saves one of my recruits from certain death.

Your Local Guardian: XCOM Enemy Unknown

The other half of the game is spent managing the XCOM project from your ant farm of an underground base.

Although it involves a different type of tactics from the combat, you’ll need to use just as much strategy to make the best use of the money and resources you have available.

On a limited budget and with a finite amount of materials and staff, you’ll need to decide which research projects to undertake to discover new technologies, which weapons to manufacture, what facilities to build, where to place defence ships and so on.

Your Local Guardian: XCOM Enemy Unknown

Along the way you’ll face very difficult decisions on which missions to accept in different parts of the world. Do you take the one offering the greatest reward or do you help the country most in need? If the panic level gets too high in a particular country, that nation may pull its monthly funding from the XCOM organisation which will hamper your progress.

It can be a daunting game in some ways because whether it’s on the battlefield or in the HQ every little decision matters in some way, but it’s also great to have a lot of choices and to live or die by how well you navigate through them.

This version of XCOM from Firaxis and 2K is an iPad and iPhone port of the game of the same name which won much praise last year on its release for PC and consoles.

I’d not played the game until now so I can’t do a direct comparison but by all accounts it’s very close to that earlier version, minus some of the visual flair and maps as well as currently lacking the multiplayer mode which apparently wasn’t very good anyway.

With what it’s got this is one of the best looking and most sophisticated games on iOS and is probably the closest thing to a full console experience which the platform has provided so far.

Your Local Guardian: XCOM Enemy Unknown

These qualities come at a price, in more ways than one. The game costs £13.99 and takes up more than 3GB of space.

Some people may baulk at the outlay, which is very expensive compared to most mobile games, but it’s worth bearing in mind the game still costs less than its console and PC counterparts. It also provides many more hours of content than most other mobile games, and it’s so far completely free of in-app purchases.

With horrible pricing models poisoning the mobile market in my opinion, it’s nice for once to be able to pay one price for a complete high-quality game.

The huge storage demands have caused a bit of a headache with managing games and apps on my iPad. It’s not a huge issue for now but could become a problem for people if other big, premium titles are put on to iOS.

Your Local Guardian: XCOM Enemy Unknown

In its current form the game does have a few glitches.

For one, moving the camera around to pan the map, zoom in, switch between elevations or see inside buildings is very clunky to put it politely. Other than this, the touchscreen controls and user interfaces on the different screens are overall very good.

The other main problem I’ve had is the game crashing on me numerous times. Having to sit through a minute-long loading sequence to get back into it is very annoying.

Another thing which could be perceived as a negative is the game not being ideally suited to on-the-go gaming, despite having been released for mobile devices. Missions can take quite a while to complete so it’s not perfect for playing in short bursts, while it’s also a battery drainer which could pose difficulties when trying to play on longer journeys.

In spite of these blemishes, XCOM: Enemy Unknown is still a terrific game which shouldn’t be missed by strategy fans who want to play one of the genre’s best titles of recent times on their iPad or iPhone.

It’s challenging, complex and thoroughly enjoyable – the type of game you can easily while away hours at a time playing (at least if you’re near a charger).

Nobody wants a hostile alien invasion, but if saving the world is this engrossing then I’m not against the idea.

XCOM: Enemy Unknown, you’re hired.

Verdict: 9 out of 10

Out now for iPad and iPhone – tested on iPad 2