Riding the elevator down into the depths of an unassuming textiles factory, its glass walls afforded me a glimpse at what awaited on the floor below. A handful of armoured FEMA agents were dotted around, either on patrol or huddled in a small group to the left. In the centre of the room, a rhythmic mechanical thud signalled the familiar presence of an unwieldy ED-209 replica, with its pair of slowly rotating turrets surveying the open, multi-level storage area. As the lift doors pinged open, I darted for the cover of a nearby raised platform, eyes fixed on the HUDs pulsing suspicion meter. Nothing.

Up above laid a series of catwalks, from where a red sniper dot flirted perilously close to my position. I pulled up my inventory and selected one of the two gas grenades I’d stolen from a newly-unlocked cabinet. Leaning out from cover, I tossed an explosive towards the amassed troops, whose immediate rasping was just enough of a distraction to break for the central stairwell, by now hopelessly unguarded. Suddenly, a piercing siren began to ring out. My pace quickened as I ducked from shadow to shadow, timing my steps to avoid the curiosity of the lingering two-man patrol. Reaching the relative safety of the far side, I crawled slowly back down the stairs, now standing across from where I’d started.

A solitary guard lingering close to the exit, completing a cursory lap of the area; deliberate looks around and behind as he went. He Paused nearby and I held my breath, convinced he’d seen me. A moment passed. Then two. Finally, he turned back towards the door and I exhaled, inching out from behind the railing to strike him in the back of the neck, sending this 3-days-to-retirement badge crashing to the floor with a bone-crunching thud that left him otherwise unharmed. As a nearby surveillance camera began its slow sweep back towards the door, the body was already halfway back into the darkness. Somewhere in the distance I could hear agents muttering about another false alarm. They hadn’t found their unconscious friend yet, but they would soon enough. By then, I’d be gone.

Set in a dystopian near-future, the world of Human Revolution has yet to be scarred by the events of the first game, but trouble is brewing. The nano augmentations of the original are preceded here by biomechanical ones, available only to a privileged few who can afford them. You play as Adam Jensen, a security officer for Serif Industries, whose pioneering research has drawn widespread criticism from an increasingly activist public. On the eve of a major conference, the company is attacked by mechanised assailants. Your girlfriend and her research team are kidnapped, and a mysterious mercenary leaves you for dead. In the haze of a surgical suite, your shattered body is rebuilt in the manner of Darth Vader, reanimated through the power of science and lost love. You awaken months later, now fully augmented. With only the first breadcrumbs of a wider conspiracy to hand, you set out to find not only who was behind the attack, but what became of those that were taken.

Your base throughout the game is Detroit, home to the sprawling complex of Serif Industries. Like a home world incarnation of Mass Effect’s Normandy, you return periodically to get mission updates and idly snoop into the lives of your co-workers. One of the great things about Deus Ex was the wealth of seemingly innocuous information it provided, and Human Revolution continues that tradition. Office break-ins are a trove of e-mails and PDAs teeming with gossiping irrelevancies, which you’ll shamefully gorge on before demanding still more. In doing so, you find your perception of certain characters changes, as with Frank Pritchard. Up until then, his superior intercom chatter was a lecturing bore, facilitating a Zen achievement for players who resisted the urge to quick-save and disembowel him, Wolverine-style. But when you hack into his computer and find he’s just another frustrated TV writer, it all suddenly makes sense. Far from the haughty Linux nerd you dismissed him as, he’s really just Bubo the mechanical owl, spending his nights getting all bent out of shape over ‘I Love Lucy’ reruns.

Thrown into the world with an array of objectives, it would seem all too easy to wander where you shouldn’t and end up thwarted by locked doors, overwhelming force and terminals you can’t yet hack. Human Revolution streamlines the process with an on-screen marker that guides the player towards their next objective, be it related to the main storyline or one of the supplementary quests that present themselves on the streets outside of Serif. All completely optional, they add to a sense of Eidos having imbued their world with personality and challenge just because. To give you some idea of the game’s ambitious scope, my mostly linear play through of the key missions took around 20 hours. Given the amount of content I left on the table – little of which resembles Mass Effect’s many-planets grind – it’s clear the mantle of adventure laid down by Warren Spector more than a decade ago has once again been picked up.

An unintended consequence of that ambition is that much of it can all too easily go to waste. One of Mass Effect’s smartest tricks was its notion of a continuing world: one in which players could visit planets long after the game was complete, either to finish side-missions or just reflect with characters about the hell you’ve been through. In contrast, to leave any of Deus Ex’s four locations is to draw them to a conclusion, preventing you from ever coming back. When the cultural melting pot of Singapore (to name but one) simply begs for such an extended exploration, that you can’t at least shuttle back and forth seems a strange oversight.

Thankfully, the time you do spend in each area is a triumph of experience and design. Seamlessly integrated tutorials help newcomers to familiarise themselves with the game’s core mechanics, from stealth right through to the intricacies of hacking. A now standard feature of the genre, this particular hacking sub-game seems an impenetrable one at first, owing to spider diagrams that play host to hubs, viruses, nodes and any number of other technobabble smokescreens for ‘Click on these icons before the timer runs out’. In practice, their mastery is relatively straightforward, yet never without a degree of panic. Playing it safe by only attacking the relevant node (be it for camera control, e-mail or otherwise) is tempting, but doing so comes at the cost of any bonuses awarded for capturing adjacent points, itself complicated by the possibility of a countdown being triggered by any one of them.

The key to your success lies in the return of the series’ hallmark – augmentations. Presented in a clean, straightforward interface, the enhancements are broadly divided into the physical and mental, offering improvements to your hacking abilities (either speeding the process up or lessening the threat of detection), increased strength, or protection from EMPs. The more assailing amongst you will welcome the additional offensive selections, perhaps best demonstrated by the wanton destruction of the prototype Typhoon system. Should you ever find yourself neglecting a labyrinthine ventilation system in favour of the more direct approach, you can have Jensen lay down a ring of explosives in an impressive ripple effect, upending and destroying anything within range. Unsubtle as it is, you find that sort of thing tends to comes in handy when the game forgets itself and duly decides to have you start killing people.

It does that a lot more often than you’d like. Which is to say, at all.

Paying a little too much reverence to Deus Ex’s unfortunate targetting of Anna Navarre and laugh-a-minute Gunther Hermann, Human Revolution undermines its freedoms by subjecting you to not one, but four end-of-level bosses. Remember that invigorating cat-and-mouse game I mentioned at the start of the review? A moment of ingenious design, triumped over by pure stealth and cunning? Well, it’s bookended by a boss who arrives with all the pomp and circumstance of a mid-chapter Resident Evil villain, save for the disappointing absence of emerging tentacles and the President’s daughter by his side. And that’s just the first one. A later encounter is rendered almost impossible by virtue of a decision you innocently made hours before, and the grand finale proves so stupefying and appallingly conceived that I spent the duration running around entirely at a loss as to what I was trying to accomplish. You don’t even trip over the solution, so much as it happens while you’re doing other things. It’s the kind of insufferable design that reminds you of not only how far the medium has come, but how far it hasn’t: how, at some fundamental level, gaming never really left the arcade, and how we’re all still sat there pumping in quarters trying to defeat the evil Gelatinous cube.

It wouldn’t be so bad, but Human Revolution goes to such great lengths to prove itself an otherwise inventive and surprising game. The first mission is typical, and seemed easy enough on first glance: infiltrate a laboratory, secure the technology in the basement, and rescue some hostages. Where possible, I tend to favour a mixed-stealth approach in which I stay largely out of sight, yet not afraid to crack some skulls when appropriate. And, sure enough, the game let me proceed in just such a manner right through to the end of the mission, where I came across a terrorist leader, gun pressed to the temple of a distraught employee. On screen, I was given three dialogue options: attack, convince him to surrender, or let him go in hopes of better odds another day. There are no flashing prompts that single out any one action as decisive; no click-here-to-be-a-badass notification. In the end, I told him he could leave just so long as he didn’t hurt anyone. He nodded his agreement, and backed out of the room.

The first I knew about it were the gunshots. Only later did I see their bullet-strewn bodies lying helplessly on the ground outside. I tried to justify myself to a Serif helicopter pilot on the way back; telling her I couldn’t possibly have known. But it didn’t help, and I felt a twinge of guilt for a character I’d never seen before. When so many games struggle to lift their incidentals beyond collateral damage, here was Deus Ex forcing me to second-guess a throwaway decision just an hour in. Something similar happens later on too, only that time it isn’t even presented as a choice. If anything, the game expressly rules intervention out. Do nothing, however, and someone you care about dies. It matters too, because when you need their help later on in the story, they won’t be there. Suddenly, even the most trivial of objectives start to feel a whole lot more important.

That’s really what Deus Ex is about: empowering the player to make choices and live with the consequences. The only constant is your objective. Everything else – the route, the means, and the bodies you to choose to leave behind – is left up to you. To a certain kind of player, a brightly-lit medical facility near Shanghai is a contemporary warren of laboratories, offices and patrols fit for exhaustive exploration. For others, the open areas suggest anarchic freewheeling: a chance for the cathartic intervention that comes from picking up a hacked turret and strolling through a bustling city with it. What mischievous delights await enquiring minds of the murderous kind.

Everyone else is going to spend a lot of time dragging bodies around and waiting patiently beneath rotating cameras, but isn’t that part of the fun? That quite disproportionate buzz that comes from scouting out patrol routes and eliminating guards one by one, listening in as their fellow stormtroopers radio for help? I live for that kind of silent triumph, and for all the completionists out there – I recognise you from the meetings – a veritable bounty of hidden treasures awaits. There are even two achievements specially geared towards our affliction: one for complete pacifism, and another for somehow going the entire game without setting off a single alarm. Suffice to say, I didn’t get that one.

Boy was I pissed.

Much as the game is a grab bag of elements, I was most often reminded of Mass Effect; perhaps now the most obvious reference point for a whole generation of gamers. In terms of presentation, there’s little doubt that Bioware continue to lead the way. The environments that make up Human Revolution are smoothly rendered and full of gorgeous detailing, but many of the character models seem to have barely advanced beyond those of the original. Elsewhere, Jensen does his best to single-handedly drag gaming back to an era of arms-perpetually-folded, mid-90s tough guy protagonists. Developers Eidos don’t seem to have considered even the advancements of Half-Life 2, let alone the quantum leaps made by Mass Effect in recent years. Whatever motivations saw fit for them to cast the player as a trench-coat stiff in the mould of Neo as voiced by Batman, it makes the cutscenes a laughable spectacle, when in Mass Effect I dare say they were the most enticing part.

Then again, maybe that’s the point. Much as we’d like every title to bask in the warm glow of Bioware’s mastery, their games as anything other than interactive melodramas are several leagues behind the accomplishments of Human Revolution. Focusing on its handful of faults risks getting so caught up in minutiae that we lose sight of a quite startling achievement. True, few moments live up to the mindfuck of UNATCO troops converging on Paul Denton’s apartment. Yet in a medium beset by artificial barriers, the game is both a welcome return to the non-linear design philosophies of old, and a shot in the arm for a genre that has come to mistake Mass Effect’s soap opera for compelling, meaningful gameplay.

For those players that missed out the first time, Human Revolution is a chance to experience what everyone has been raving about these past 10 years. The rest of us can revel in the clever foreshadowing of events still to come; all the references to Page, DuClaire and Manderlay. The mind boggles at the sheer scale of the world, and the countless ways in which you can approach it. Everywhere you look is a clever detail, or something new to see, and Deus Ex not only rewards repeat play throughs, but demands them. Human Revolution is a bold vision of our transhumanist future, and a breathless, once in a generation, refreshingly adult entertainment.