Ubisoft has picked the perfect time to take the wraps off Watch Dogs. In an E3 that's provided precious little in the way of innovation or excitement in the action adventure space, its brand new IP has been one of the few freshly announced titles to generate any palpable buzz on the showfloor.

However, under closer inspection in an invite-only broom cupboard tucked away in the publisher's booth, there's plenty of evidence to suggest Ubisoft Montreal's hugely ambitious open world adventure would have grabbed plenty of headlines even during a vintage year for LA's annual gaming expo.

For those who haven't pored over the demo footage shown during the publisher's press conference on Monday, here are the basics. Watch Dogs plays out in a near-future Chicago where all digital devices are linked by an enormous clandestine data network set up to allow private corporations access to every single scrap of data linked to an individual person.

Protagonist Aidan Pierce has somehow hacked into that grid and, via his magical PDA, can manipulate almost every digital device in the city, from cell phones, to security cameras, door locks, traffic lights and public transport routes. For reasons not fully explained, he's duly leveraging that power to kick back against an as-yet undefined foe.

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How exactly does this translate to gameplay? In the demo Pierce attempts to gain access to an art gallery opening where he's been told a target called Demarco is holed up. He sneaks his way in by disrupting the mobile phone network, forcing the bouncer to wander off in search of a better signal. Once inside Pierce then scans the crowd in search of an employee of his target and listens in as she calls her boss, discovering that he's currently on route to the venue in his car.

So, Pierce runs outside and, with perfect timing, ensnares his enemy in a massive pile-up by tinkering with nearby traffic lights. Following a brutal shootout he jumps into a vehicle and tears off across the city, losing his pursuers by raising a drawbridge across the Chicago River.

While the action in the demo was clearly heavily scripted, it's not difficult to see the enormous potential behind that core conceit of using an entire city as your weapon. Though he was light on specific details, producer Dominic Guay promises that there will be countless ways to achieve your various goals in the finished game.

"One of the team's big frustrations with the E3 demo is that we can only show one path. The fact of the matter is we could have eliminated Demarco in hundreds of other ways. We know he is coming so we could have waited where he might have parked and hit him there. You saw we can also open up drawbridges on the Chicago River so maybe we could have used those instead.

"We showed the traffic hack as it's seemingly a really small action but what it creates is so powerful. It's a perfect example of how when you have power over the networks you have huge power over the city."

Like so many other games showcased at this year's E3, Watch Dogs is unsparingly violent. The demo sees innocent bystanders gunned down before Pierce brutally executes his target without a shred of remorse. Guay insists that this unflinching brutality is a vital tool in conveying the game's sophisticated, adult themes. And what's more, he promises, the game will always temper bloodshed with real, dramatic consequences.

"We have an ambitious goal on this. [Project lead] John [Morin] has a motto: make it less Michael Bay, more Michael Mann; less Transformers, more Heat," he says.

"There is collateral damage - there are bystanders who get shot because you decided to start a fire fight in the middle of the city. Every player is going to react differently to that. We're not going to tell you it's good or bad. What we hope is that if we're realistic in the treatment of violence and what it does to the city and its people, then you'll set your own boundaries. At the very least you'll realise the consequences of doing crazy things."

What Ubisoft didn't show during its presser is a companion tablet app that adds a tantalising additional layer to the action. As well as a host of stat-tracking and social features, the app will supposedly facilitate asymmetric real-time multiplayer, where one player will embark on a mission on the TV screen while the other either helps or hinders their progress by tweaking the digital environment via a fully-realised 3D map on the tablet app.

"The core of it is that we want to keep the same fantasy: control the city from the palm of your hand," Guay explains.

"A lot of games have already done the mobile thing, but only as a way to access game stats. For us, that's not enough.

"If you get on the bus we want you to be able to continue growing your control over the city and getting benefits from that in the game. We also want you to be able to go into the living room and play with other people who are playing on the TV. That's core for us.

"And it's also a way of connecting with other players. There are going to be a lot of consequences to growing your ability to connect with other players."

Almost as ambitious is the studio's bold approach to ephemeral emergent gameplay. Guay explains that aside from Watch Dogs' main campaign you'll be able to create your own side missions on the fly and interact with the city in a hugely dynamic and open-ended way.

Every single person wandering Chicago's streets can be scanned and will boast their own unique backstory, however mundane it might be. You can then react to that information as you see fit, slotting yourself into their lives in a variety of ways.

"We don't need to set specific mission objectives," insists Guay.

"I'll give you an example. You'll walk around the city, profiling people through the surveillance system and you'll see a guy who is convicted of some horrible crime - a multiple rapist or whatever. You see him walk down an alleyway and decide to follow them. You have a gun, you have all these abilities - what will you decide to do with that knowledge? That's the player's choice, and they're going to have to face the consequences of those choices too."

Impressively, all these tiny subplots are individually crafted by the game's writers rather than being randomly generated.

"What's important for us is that it doesn't become a sea of information that's not interesting. You'll find very interesting things that you'll want to follow and look at," he continues.

"The game has a structure where you have a clear path with strict objectives, but we know a lot of players are going to want to explore the digital side of the city too and they're going to find a lot of opportunities for side objectives to set themselves."

Guay is cagey when we ask exactly how large Watch Dogs' urban playground will be, but promises a substantial sandbox to mess around in.

"We don't give specific numbers - the main reason is we still want to be able to tweak that to optimise the fun - but it's pretty large," he explains.

"What you saw in the demo was just a little street corner in The Loop in Chicago but you can go way beyond that - you can cross rivers and explore much bigger lands. Our cars go very fast - they go up to 180 kph. You can't have a small city with cars going that fast."

The other major talking point is of course the game's hugely impressive visuals. Seen up close, rather than on the big screen during Ubisoft's press conference, the level of detail is remarkable. Pierce's trench coat billows in the wind, the rain sweeps and swirls through the streets, extravagant muzzle flair lights up gun combat and generally the city teems with life. Guay makes it clear that the demo is running on a PC but stresses that game will also come to PlayStation 3 and Xbox 360.

"We're not shipping this year. By the time we ship we'll be on multiple platforms, including Xbox 360 and PS3," he says.

But how?

"To be honest, we have a kick-ass team of guys working on tech for consoles. Most of them have been doing it for 10 years, working on Assassin's Creed and Splinter Cell and all those brands, and have a lot of talent. We're really committed to supporting as many platforms as possible."

Is he bluffing? We wouldn't be surprised. It seems inconceivable that the game, as shown, could be squeezed down to fit on current gen consoles, especially when you take that ambitious cross-platform smartphone play into consideration. Time will tell, and we're ready to be proved wrong, but this could well be your first glimpse at a next gen experience.

There are still plenty of questions that need answering. With Pierce seemingly having such an enormous range of powers at his fingertips it's hard to conceive how Ubisoft plans to avoid overwhelming the player. How much choice will there really be? Will the sheer scale of its ambition eventually railroad the designers down more linear and scripted pathways? Are those eye-popping smartphone features just pie in the sky? We'll see. However, if it does manage to deliver on its grand mission statement, Watch Dogs promises one of the most intelligent and imaginative twists on the action genre in years. Godspeed, Ubi.

Watch Dogs is finally out, and we've got an essential game guide to help you beat the trickier missions.