As far as we know, Prototype is the only game that enables you to karate kick a helicopter right out of the sky. As a result, Prototype went on to become 2009's best-selling new IP, shifting 2 million copies. It was what developer Radical Entertainment called “the ultimate power fantasy”, in which you could not only kick a helicopter, but as angry mutated escaped test subject Alex Mercer, you could run up the side of the Empire State Building, vault off it, glide and elbow drop a tank. “No other game lets you do that,” says Producer Jonathan Lim as he prepares to show us Prototype 2 behind closed doors at E3.

Lim notes that Radical isn't resting on its laurels for Prototype 2 though, and is looking to make the game even more of a power fantasy, with a “clear road map of improvements.” This time around you won't be assuming the role of Alex Mercer, but you'll be turning the tables upon the previous game's protagonist as Sergeant James Heller, who returns home from a tour in Afghanistan to a decimated New York City where he finds his family butchered. Imbued with the same strain of mutant powers as Prototype's original protagonist and with nothing left to live for, Heller sets out on a mission to eradicate the virus and kill Mercer. Consequently, Heller embraces his new powers, seeing them as a means to an end rather than a curse. That means that he's more proactive than Mercer and far less mopey.

As Heller, you'll also always have a clear purpose and understanding of the task at hand with your objective always down in the bottom right corner of the screen, so you'll never be twiddling your thumbs wondering what to do next. Even Prototype 2's 'NYZ' or 'New York Zero' is divided into separate zones that each have a colour-coded severity of viral infection. The entire NYZ is quarantined from the rest of the world after 14 months of biological warfare, so the red zone is the most infected part of the urban jungle, filled with the most aggressive and frightening mutants, while the yellow zone is a quarantined shanty town settlement, reminiscent of Children of Men or District 9's shanty towns. The green zone meanwhile, is a comparatively safe area closer to the New York you know and recognise, only it's lorded over and ruled with an iron fist by the unscrupulous Blackwatch. The first part of our hands-off demo opens slapbang in the middle of the green zone, where Heller is standing high on a rooftop watching a violent scene unfold on the street below him.

There's a crowd of people trying to gain entry to a safe area guarded by a group of Blackwatch soldiers, and as their request to pass through the barriers is flatly denied, the angry throng starts to get a bit raucous. At this point, the Blackwatch troops callously open fire on the crowd, executing them all in cold blood. Witnessing this, Heller takes action by stealthily picking off one of the guards, mimicking him and shapeshifting to create a disguise that enables Heller to get as close to the guards as he likes. He then takes down another troop and unleashes an incredible Bio-Bomb move by holding B, causing an explosion of tendrils to emanate from his mutated body, impaling the enemies around him. This can also be used to create a distraction, but no doubt taking out multiple enemies at once will prove the more popular choice for most players. Like Mercer, Heller can also consume foes with a tap of the Y button, getting a look at the character's memories in the process. So, when he consumes a scientist using his slimy tendrils, it initiates a cut-scene recapping what he's seen in the last few hours, revealing tidbits of useful information.

Using the Blackwatch's network, fittingly called Blacknet, Heller can also tap into research and access the database to find out more about operations and use the intel to hunt down targets and shut them down. Hunting represents a new gameplay aspect in Prototype 2, so you can emit a sonar pulse by pressing the left bumper to pinpoint your prey. In this case, it's a man named Lt. Barry Pollock, who holds the key to Heller's progression. Once again, Heller takes to the rooftops to get an overview of his surroundings, jumping between buildings with uninterrupted fluidity while his sonar pings back and forth between him and his target. Running up a building, Heller drops into the area and makes short work of two heavily armoured APCS, picking from one of three context-sensitive options mapped to the X, Y and B buttons. Hitting X for 'weaponisation', Heller tears the turret from one of the APCS and uses it to fire rockets at the hostiles in the area, before consuming the target, then fleeing to the rooftops and adopting a disguise to go incognito.

In Prototype 2, you'll be able to customise Heller's mutations, choosing the perks and augmentations that best suit your preferred style of play. The demo offers either 'Bird of Prey' that offers an extra air dash to make traversal and locomotion even more fluid or an 'Adrenaline Surge' that increases Heller's jump height. It's entirely up to you which abilities you opt for though. With new mutations equipped, the final part of the demo shows the virus-infested biohazard lairs that you'll come across, where there's numerous monsters to be killed and a huge Hunter enemy to consume, as well as fat oozing bags of pus called Juggernauts. It's a hive of pulsating, writhing infection-ridden flesh in the lair, so holding X or Y for a charge attack helps tear through several enemies at once, while deploying your tendril tethers creates a kind of web that slows down the foes around you. Using his blade arm, Heller can also dismember enemies and upon clearing out the lair, he's rewarded with an upgrade to his razor-sharp appendage.

There's what Lim calls “global improvements” to the combat system in Prototype 2, and it's clearly evident on screen. The action has been slowed down slightly, so that's it's not quite so confusing and chaotic, and there are longer attack tells, allowing you to read and react to the threats around you. Heller also has a tactical dodge move now, so he can leap to safety should things get too hairy. Lim wraps up the demo with a first look at what is currently being tentatively called 'Tiny', an enormous behemoth-sized enemy with a gigantic stomping left arm and blade, but that's about all Radical is prepared to show of the game for now. That's fine by us though, as we've seen enough to get a good feel for what Prototype 2 is all about and it looks like Radical Entertainment has really taken on board the criticisms levelled at the first game, addressing its shortcomings with what looks to be tighter, more refined gameplay and a greater degree of fluidity. Most importantly though, none of this looks to be to the detriment of that core power fantasy that only comes with uppercutting a helicopter and kicking a tank over a building, which can only be a good thing.

Prototype 2 is slated for release in 2012.