About two hours into Army of Fistbump 3, I developed a theory about the game. At the start the two main characters are hit by an RPG ambush in Mexico. The game then flashes back to our heroes as they're trained up to be ruthless, ass-kicking mercenaries, bent on taking on the cartel that set them up. They do this by killing more people than every single armed human conflict combined. As they fight, endlessly, through a repetitive collection of dull brown tunnels, dull brown markets, and dull brown enemy strongholds, they sometimes become invincible, and their guns get infinite ammo, for reasons never explained. And then everything, EVERYTHING, they shoot explodes and everyone's limbs blow off in a shower of gore.

Clearly they must be dead, I thought, and what follows must then be the dying revenge fantasy of the leads, with the developers using that framework as a big joke at the endless violence/total nonsense on display in video games; including, of course, the last two Army of Two games. It has everything: bland levels, stupid dialogue, over-the-top kill animations, poorly-implemented online co-op, zero-dimensional characters, which are called - no shit, Alpha and Bravo. A and B, like in old NES games. There are meta references by both characters about the nature of video games and how they operate. An obligatory driving level makes an appearance. Enemies run into the path of your car, and when they do, again their limbs just fly off in different directions. Ha ha ha, I get it, driving sections are rubbish. Big Boi from Outkast is in it, for no apparent reason save 'video games'. It's glorious.

Then, roughly 10 hours of shameless (s)laughter later, I realised it probably wasn't a joke. The references to video game clichés are lampshades to throw players off the fact that they're too creatively bankrupt to think of anything else other than red barrels or telegraphed plotting. Which means, and this is incredible, that EA has created something this on the money by mistake. Despite all of its flaws, Army of Two is one of the most enjoyable shooter experiences I've had in a while, because it's so stupid, yet somehow works as an effective critique of modern shooters. Incredible.

Objectively speaking, most of the game is pretty terrible. The story is total guff: some noise about crusading politicians who need mercenary help to fight the cartels of Mexico. This, of course, is just an excuse to shoot everyone, ever, dead. There are whole dialogue exchanges that comprise nothing more than the sort of grunts often made by professional wrestlers, and a supposedly emotional moment later has all the effect of a fart in a heavily-congested train carriage.

For a game that relies heavily on online co-op, it makes it pretty difficult to seamlessly play online. Anyone joining or leaving your game punts you back to the last checkpoint. There's a focus on upgrading your toys (sadly, the OTT flair (zebra-print 'camo'!) of the last game is gone, replaced by classic gear bullshit upgrades), but to do so you have to head back to the armoury. Again: Total Nonsense.

In-game mechanics fair little better. Co-op actions barely evolve from helping someone step-jump or pushing a van. You're told that flanking is the key to victory, and yet cover is so difficult to get in and out of (sometimes not responding to your button presses) that you'll often be killed not in valiant battle but jabbing A to hide. The levels themselves are so bland and brown that it all meshes into one, like a particularly unmemorable shopping experience through Next's autumn-winter menswear lineup.

And yet, I couldn't stop playing it, because it made me laugh - genuine laughter, not snooty guffawing - at how over the top it was, in the same way that Commando might do. The shooting in Army of Two has, for me, always been very solid. There's a weight to it (and your characters) that makes it feel like you are a death-dealing instrument of doom, and it actually feels like you're firing a gun, not a peashooter.

The Devil's Cartel takes this to its logical conclusion with Overkill mode, the centrepiece of the game and a mechanic so good, so fucking honest and on the money about what a lot of people actually want from the shooter industry, that it now must be in every shooter from here on out.

Players get points for performing well in combat - co-op actions, flanking, headshots, that sort of the thing - and when enough of these tot up Overkill becomes available. Deploy it with a jab of LB and Army of Two becomes incredibly good fun.

During Overkill you are invincible, and have infinite ammo. For a game mainly about hiding, this is quite the turnabout. What follows is the sort of gun-porn that makes the jungle-mowing scene in Predator blush. Fair play to EA: the environments might be utterly forgettable, but they explode beautifully.

And they will explode. Once Overkill is engaged, it is near-impossible to take your finger off the trigger, especially if your partner does it at the same time, activating, yes, DOUBLE OVERKILL. As the environment rips to pieces and enemies de-limb in slow-motion, the two of you will no doubt be giggling like schoolchildren at the mess you've made: bits of plaster launching out from supporting walls, stonework crumbling, men suspended in mid-air while you shoot their limbs off.

That probably sounds quite nasty. Quite the opposite. There's no way any of this could be mistaken for real-life. It's so dumb it is brilliant. As a reference, it's something like this, over and over again, and three times as funny:

Because Overkill must be expended once it's activated, there will be times when, because it's so satisfying, you'll kill everyone and just be shooting empty rooms. Shooting empty rooms. Madness. Often times you'll be shooting over dialogue being said in slo-motion, which means that, finally, the dialogue is actually explosions.

With a friend sitting next to you on the sofa, Overkill turns a tired, forgettable shooter into something completely different. The poor AI, banal settings, and frankly rubbish cover pale into insignificance when you're playing what is, in effect, a 3D version of old-school shooters such as Contra. It's Commando, but now you are John Matrix (John Matrix...superb.)

A lot of what comprises Army of Two: The Third is total crap, and yet I had a lot of fun playing it. We don't know how EA has done it. They probably don't know how they've done it. But they have. And I'm glad they did.

Version Tested: Xbox 360

Completed campaign on Normal difficulty in around 10-12 hours.