As the old saying goes, "If it ain't broke, don't fix it." In the case of Borderlands 2, most people would be satisfied if Gearbox followed the idiom and gave us more of the same loot-n-guns action we enjoyed back in 2009. On the face of the game's first showing, however, it seems as if the developers are aiming to up the ante.

That's not to say this sequel is a massive departure; the cel-shaded look is as distinctive as ever, while the anarchic chaos that unfolds before our eyes offers immediate proof that the game's tone remains gleefully mischievous. Under the hood however, it's clear that there have been several revisions to the core mechanics, the results of Gearbox's self-proclaimed intention to "Gut, replace or revamp" its own successful formula.

Let's start with the guns. There are still thousands of them, but this time the differences between manufacturers will be more pronounced, to the extent that you'll instantly know who made a given weapon on the basis of the way it looks; beyond this, you'll also know what to expect when you first pull the trigger. Vladof guns have an AK47-style Russian aesthetic and all come with gatling barrels, their rate of fire accelerating from a slow rattle to a fearsome hailstorm of hot lead. Tediore, dubbed by Gearbox as "the Walmart of guns", offer disposable firearms that you throw away rather than reload: the weapon effectively becomes a grenade, with the strength and effect of the explosion depending on how much ammo was left in the clip. Torgue guns appear to exclusively fire explosive projectiles, while the new Bandit-class arms offer massive clips and a junkyard, cobbled-together look.

As we already know from the first teaser image, Borderlands 2 will also offer us a new set of character classes in place of the original quartet. One of these newcomers will be another Siren - this one's called Maya - but unlike Lilith, her power doesn't involve phasewalking. For the time being, Gearbox is only talking about Salvador, the Gunzerker, and even then we've only been given a brief glimpse of his potential. As an evolution of Brick the Beserker, Salvador's class skill revolves around dual-wielding - a talent that looks to be just as devastating as you'd imagine. Expect this skill to go hand-in-hand with the accentuated differences between gun types.

We didn't get much opportunity to inspect Salvador's skill tree, but it seems that there will be more abilities to choose from this time. Each subset of perks now gets its own Y-shaped tree, with what looked to be about a dozen options on each - I didn't get time to count. Sal's skills include Die Hard, an old favourite of Brick's, plus Asbestos (which reduces negative status effects) and the excellent-sounding Just Got Real, which increases damage done with all weapons. I'm pretty sure that's what they do, anyway: I had only seconds to note down the options as the demonstrator flitted past them.

As for the original characters, they'll return as part of the story - a tale set five years after the first game that sees you seeking revenge against a chap named Handsome Jack. Apparently he stole all the credit for finding The Vault in the previous storyline (well, what passed for a storyline), and as a result he's been trying keep Brick and friends from blabbing their mouths about what really went down.

For the time being, it's the revised enemies in Borderlands 2 that are stealing the show. Our first new foe is the Bullymong - a kind of six-limbed gorilla creature that will dynamically pick up objects (or rip up bits of scenery) and then lob them at your head. We're also told that the beasts will scale high areas and then leap down onto players to inflict fall damage. Enemy AI has been a focal area, resulting in smarter attacks, in a greater variety of attack styles. In the demo, the clearest example of this was to be found in the Marauder bandit, a large thug who makes intelligent use of cover, retreating to find allies when you do succeed in putting a few plate-sized holes in his grubby frame.

Beyond the AI boost, foes now have different statuses which will be obvious from their behaviour. If they get badly wounded, they'll limp, and if they're really close to death they'll shoot at you from a downed position. This looks particularly slick in the case of certain Hyperion robot foes, who pull off an impressive last-gasp Terminator impression. Leave these guys for too long, however, and your risk them being healed by Surveyors - floating bots who can restore their chums to full health surprisingly quickly. In short, expect combat in Borderlands 2 to involve a lot more strategy, if only in terms of whom you decide to shoot first.

I'm pushed for time here, and in my hurry to cover all the new inclusions I've strayed away from focusing on the more outlandish aspects of the demo. As I've said already, the tone remains as over-the-top as ever; there's no doubt that Gearbox is doing its best to completely out-do the splatterhouse humour of the first game. The latter half of the gamescom presentation revealed that the Hyperion corporation, who appear to be one of the major villains now, have the ability to rain down robot reinforcements from a nearby moon. You'll be halfway through a battle, gaining the upper hand, and suddenly a load of new threats will come crashing down right next to you.

My personal highlight was a boss enemy called Nomad - a giant robed figure who strode into battle with a massive shield... a massive shield with an angry midget strapped to it. This being Borderlands, it's possible to shoot away the midget's restraints, temporarily gaining you a furious, pint-sized comrade. For all the new tweaks and features, it's reassuring to see that Borderlands' spirit has been left untainted.

Borderlands 2 is due for release in 2012 on Xbox 360, PS3 and PC.