At the outset of Radical Entertainment's game Prototype, black wormy tendrils slither around a taxi, nudging it, goading, as not-quite-vigilant-enough policemen patrol a decimated city square.

The city - another freeform version of Manhattan - is flushed, sanguine, the colour of a torch beamed through fingers. High-rises, brownstones, and walk-ups look ghoulish, scummed with weird pustules of pulsing tissue. Half-human forms lie beside crumpled vehicles, ripening in the heat. Ravens roost on corpses like carrion omens. "I want to be a part of it" New York this version's definitely not.

You're the reason for all of it. Some call you a killer, others a monster or a terrorist. You call yourself all of the above. Three weeks ago, someone loosed a lethal virus in Penn Station and you woke without explanation on a slab, memoryless, about to be autopsied.

Now you hunt and consume, vampire-like, dissolving passersby like coffee poured over sugar, slipping into their skins as skillfully as a thespian swapping costumes. Your name is Alex Mercer, an accidental superhuman, an amnesiac with sociopathic tendencies, the only force powerful enough to save the city, but only if you can save yourself first.

Sound a trifle like Naughty Dog's inFAMOUS? That's the popular sell, but once you've graduated past the introductory missions, you realise just how much it's not. inFAMOUS is about ethical choices that change the story's course, whereas Prototype lets you choose between living and dying and to heck with moral niceties.

inFAMOUS gives you exceptional abilities with power checks, whereas Prototype is a galloping, soaring, superpower extravaganza. In inFAMOUS you clamber deliberately up realistically ledge-littered structures, whereas Prototype's Alex sprints breezily up the sides of conveniently flat ones.

If inFAMOUS's Cole is Stan Lee's Electro sans the neon-guacamole spandex, Prototype's Alex is more Marc Silvestri's sable-barbed The Darkness fused with Lee and Jack Kirby's otherworldly shapeshifting Skrulls, a mutating mass of coiled and writhing energy, one capable of hurtling between skyscrapers - or simply over them - like an alien projectile.

Alien-apparent, that is, but entirely earthborn. In fact Prototype's quintessential plague-story makes your ground zero for a metamorphic virus that's infecting Manhattan's populace. As Alex relates his horror-laced tale to a masked figure on top of a building, so you experience it in analepsis.

As you're escaping from the morgue at the start, you're shot but - to your surprise - don't die. You discover you can leap over walls and, soon enough, entire buildings.

Eventually you can fashion armor and weapons from your limbs, crab-leg claws to Japanese-style fantasy blades to tongue-like tentacular whips. Vehicles are everywhere, but you're limited to either destroying or lifting and tossing them. Why drive anyway, says the game, when you can fling yourself through the air, entire city blocks at a time?

At first all that power can actually be disorienting. Your inclination - or at least mine - is to fine tune, as you would playing other hyper-agile protagonists like Altair in Assassin's Creed or Cole in inFAMOUS. It's a losing proposition. Whether you're taking small jumps or bounding leaps, it's almost impossible to finesse your landings.

Defying physics, you can change angle mid-leap, but so jarringly that you'll rarely have the thumb-stick aligned in the direction you intended. The camera has a tendency to swing down and face-forward, preventing you from tracking your trajectory isometrically, often sending you just past the edges of things, wrestling control away from you until you've finished the move. In short, a bit of a clumsy mess.

But then your leaps suddenly get longer and their arcs broader, providing the space you need to sort those aerial vectors. You acquire the ability to glide considerable distances and recover almost instantly from debilitating enemy throws. Your tactical combat moves and special abilities grow powerful enough that even glancing blows impact your opponents.

You notice that the reason the game's been delaying subtracting hits from your health bar is so that you can react before it fully collapses. And suddenly everything clicks, and you realize this isn't a game about fiddling grabs and toeholds and precision maneuvers, it's a button-mashing gladiatorial smackdown. You're not some spider scrabbling gracefully across an intricately crafted cityscape, you're an amped up bull full-on charging it.

Once you've got Prototype's city-scale "adaptive parkour" under your fingers and you've swallowed the macho pill, Manhattan's more or less your oyster. The city's divided into infected and uninfected areas as well as military zones that you can explore at your leisure.

The island's been quarantined (of course) as well as factionalised - it's you versus the military versus increasing droves of mutant citizens. Somewhere in there you'll have to tango with conspiracy groups as well as, well, let's just say those "mutant citizens" come in all shapes and sizes.

Initially your missions tend toward run-in-and-thrash-around brawls, the reward being buckets of evolution (see: experience) points to help get you properly leveled up while you're acclimating. But these quickly shift toward subtler activities, like ones that involve hijacking military vehicles and tackling multi-stage rescue sorties, or which capitalise on your ability to assume the physical form of the last person you've just gobbled down.

Gobbled down? That's right, Alex may be the game's titular anti-hero, but his virally-enhanced methods are strictly sociopathic. As he endeavours to define himself and exact revenge on whatever transformed him, he'll necessarily consume hundreds of individuals, innocents and enemies alike. In fact it's a little disturbing that pedestrians aren't just expendable here, they drop like flies, and without apparent penalties.

I killed over 4,000 pedestrians in the course of a single game, not a one intentionally, yet finished the game with the score equivalent of "flying colours".

While those pedestrians were obviously just facades with pull-string hysterics, it was tough to root for myself, since in the end I had to callously treat the people I was supposed to be saving as ants.

Prototype really opens up about halfway through, once you've unlocked all the basic abilities and vehicles and the game starts throwing in little twists. In order to breach military installations or hijack certain vehicle types, Alex has to locate the proper persona for the task.

If he intends to fly a helicopter, for instance, he'll need to find a military grunt, "consume" him away from prying eyes, infiltrate a military compound, then perform a series of further "stealth" consumes that unlock the identities necessary to penetrate the military installation and pinpoint the requisite chopper pilot.

If you want to drop artillery strikes, you'll have to find and consume a particular type of commander. And if you consume special military scientists, you'll reveal the location of key figures who'll unlock aspects of the game's tangled narrative web.

Detection challenges are cleverly diffused throughout, keeping you on your toes, from the horrified panic that ensues if you shape-shift in view of someone, to the blinking viral sensors that can detect your infected presence whether you're disguised or not.

Disabling the sensors is possible, but takes speed and the ability to press a series of buttons in perfect sequence. If you're caught out, you'll have to scurry for cover, then switch to a temporary alter-ego to get the cavalry off your back.

Minor touches add a dash of drama to otherwise conventional goals. Anytime you're detected by the military, there's a chance one of the soldiers will radio for a strike team, meaning in this case helicopters. Lots of helicopters. Enough to turn a nearly-won battle into a loss, in fact.

If you can take out the radio op quickly enough, you're golden. But if you fumble, you'll have to elude the chopper squadron, or when you're powerful enough, spend several harried minutes strategically squaring off against and blasting them apart. Here's how I described choice number two last week.

...leap off a skyscraper, glide like a skydiver, fling a tentacular barbed cord from your body like a ropy black tongue, tag a nearby helicopter, then reel yourself up to pry open the door, consume the pilots inside, and man the controls. If you're fatally hit while flying, just leap from its plummeting wreckage, glide to within striking distance of the bird that got off the lucky shot, set your tentacle flailing, and repeat.

Scattered amongst the populace are "web of intrigue" targets, random citizens who stand out on your radar, popping up in downtempo moments, but also as risky temptations during uptempo ones. If you pursue and consume them, you're treated to a slice of narrative illumination that plays like a psychedelic music video with bits of background story filler.

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