Last month I got to play Deus Ex: Human Revolution, and I've already told you what I thought of the first half hour . The rest - all the juicy stuff about augmentations, social hubs, and the first proper levels was under embargo until now. So here's what I thought of the next two and a half hours.

That's when the third Deus Ex game really starts. Plenty before this point is a little worrying - an on-rails tour of Sarif Industries, some slightly off-putting attitude from Jensen, and the whole assault-rifle-only thing. But that's just an interactive intro. When we rejoin hero Adam Jensen after the credits six months later, it's a very different game.

You arrive back at Sarif Industries, in the lobby, and are free to explore wherever you like. Sarif wants you on the helipad to respond to a situation at one of the company's remote facilities, but you're not forced to oblige him in any kind of time. I wandered around the complex talking to everyone, going into every office and every floor, much the same way I did at UNATCO HQ back in 2000.

I overheard a co-worker talking trash about whether I was ready to be back at work, which let me try out the conversation system. I had the option to confront him, reason with him or change the subject, and before you confirm your choice you get a short preview of the line you'll actually say. As someone who frequently groaned at Commander Shepard completely misunderstanding what I meant when I selected "We have to hurry" in Mass Effect 2, I appreciated that. It's also just really satisfying to be able to properly chew someone out for bad-mouthing you. Jensen's kind of a dick at times, but when you've instructed him to be a dick, it's fun to watch him do it so well.

I eventually found my office, and after bloody-mindedly trying the same password that worked in Deus Ex 1 three times, discovered that my actual login details were on a datapad on my desk. There's lots of e-mail to read, from company-wide memos to messages of support from colleagues, and even a mail from the receptionist about a minor security matter she'd like you to look into. That mail starts a whole side quest about a thief in the company, one you could easily miss.

Naturally, my next stop was the ladies' bathroom. There's a running joke if you keep blundering in there in UNATCO headquarters in the first game, so I had to know if Eidos Montreal would acknowledge it. Two women in the stalls are discussing your return to work in there, oblivious to your presence, and they hint at something you don't know about your injuries and the attack that day. Intriguing, but not funny. Later, though, my experiment in creepiness paid off: tech stereotype Pritchard adds, after briefing you, "Your body's changed, Jensen, but you haven't become a woman. Stay out of the ladies'."

With the important stuff out of the way, I finally found the helipad and set off to save some lives. The mission isn't as simple as a hostage rescue: a group of anti-augmentation purists have raided the facility where Sarif was developing the Typhoon aug, the one Jensen's using when he fires out tiny explosives in every direction in the first in-game trailer. They're presumably looking to steal the prototype, and they've taken scientists hostage along the way.

It says something about Sarif, both the company and the man himself, that your primary objective is the Typhoon prototype - the five scientists with their lives on the line are secondary. It's even possible to get them killed before you so much as start this mission - if you take much longer than I did exploring Sarif HQ, after repeated warnings from Sarif himself, he'll let you know the situation has changed, and the hostages are dead when you arrive.

I laughed when I first saw Zeke Sanders, the first villain you get to face: he actually has an eye patch. But it turns out there's a story even to that. Sarif says the guy can't have been involved in the attack six months ago, since he's not augmented. In fact, he's fighting to end augmentation. But he's not quite right - a SWAT officer on the scene says he heard Zeke was augmented once.

The truth is that Zeke is a veteran, and the US military have a policy of offering free augmentation to any wounded vet who signs up for another tour of duty. Zeke lost his eye in combat, and went back to active duty in exchange for a cybernetic replacement. He got his augmented eye, but became convinced it was driving him to do the horrible things he did in war. He had it removed, hence the patch, and joined the purists.

Before your chopper lands, Sarif tells you that "The rules of engagement are your call: do you want to go lethal or not?" He's not, as I feared, asking you to set the failure conditions of the mission. The next question is whether you'd rather get close or engage at a distance: this is the weapon selection conversation you had with your brother Paul at the start of the first game, but with another level of choice. I picked nonlethal and close up - basically Hard Mode - and got a Stun Gun; a short range tazer with just a few darts. If I'd gone with long range, I would have got a tranquilliser rifle - the equivalent of the first game's mini-crossbow. Close range lethal is the Magnum revolver, and long range lethal is the assault rifle.

I was also given 6 Praxis points, level-up currency you'd never normally have this early in the game. It costs 2 points to get a new aug, 1 point to upgrade an existing one with a new feature. Most tempting: Strength upgrade to lift and throw heavy objects, Awareness aug to highlight hostiles on my minimap, Landing System to negate fall damage, Lungs to sprint longer and survive that toxic gas I discovered earlier, or Legs. The Leg aug is so good I considered putting all my points into it: the upgrades respectively let you jump higher, sprint faster, move silently, sprint silently, then jump and sprint silently.

In the end I went for Strength, Cloak, and Legs with silent movement. The walk softly and carry a big box approach. Immediately, I regretted not getting the Landing System - you start on a rooftop, and it would be beyond badass to leap off it to start the mission. But once I got down the human way - after fumbling with a ladder and falling to my death once - I found the starting area an aug playground.

The guard I landed behind gibbered and collapsed with one stun dart. Around the corner, two more were talking. I used Strength to - yes! - stack a crate near a shack wall nearby and peer over the top to scope them out. If I'd gone for the jumping upgrade for my Legs aug, I could have just hopped it. And if I'd used Brain to not be an idiot, I probably wouldn't have fallen over the wall into plain view of them both.

After a hasty retreat, my infiltration started to go more smoothly once I got the hang of hugging cover. I snuck through the next few areas - big, airy storerooms in the Shipping & Receiving wing of the building - without engaging or even being seen by any of the guards. Deeper in the facility, things got tricky enough that I had to start tazing bros. Having exactly no manual skill with a 360 controller, my preferred method was to hide in cover until they almost passed me, then blind-fire with the stun gun to minimise my exposure. This is wildly inaccurate, making it a terrible idea with a single shot weapon, but if they're close enough it doesn't matter.

Regular guns kill with one headshot, but without a mouse that's entirely beyond my talents. Human Revolution is incredibly stringent with ammo - I rarely had more than 4 rounds in a given weapon - so mowing everyone down wasn't an option either.

Whatever you specialise in, though, you can always hit them with your robot arms if you have enough batteries. A melee takedown, whether you choose to make it lethal or just a knockout, consumes one cell of power. Other augs drain those cells more gradually - each battery has a little progress bar of remaining charge - and if you've got less than one full cell, you can't use melee attacks at all. The good news is that your last cell always regenerates over time, so if you've run out of absolutely everything else - and I frequently had - you can still stalk a room full of enemies with a slow rhythm of sneaking and punching.

That battery system certainly stops you from becoming a reckless superhero. Cloak was almost useless to me, since one cell of energy only fuels it for a second, leaving you unable to punch. I can't speak for the way you'll play, but when my Cloak ran out in front of an armed guard, I was usually in the mood to punch a guy. That problem was mainly a result of this demo: you're not supposed to have augs at all by this point, so there aren't nearly enough, er, energy bars to recharge your energy beyond that one cell. I don't mean bars of energy, I mean high-calorie snack foods - that's what you eat to regenerate bioelectric energy.

Once I got the hang of punching, I tended to overuse it. I finally found the hostages, still alive in a room with a toxic gas canister ready to release. Its trigger was tied to the door I just came in through, so I had seconds to save them. I couldn't see a prompt to defuse the bomb, so I went to the hostages hoping to carry them out. All I got was the usual melee prompt - tap the button to knock them out, hold it to kill them. Well, I didn't want to kill them. Tap it is!

You're, er, not meant to punch the hostages. You certainly can, and you can even drag their limp bodies away. In fact, since I had Strength, I could have easily tossed this unconscious middle-aged lady out of the room with some force. The trouble was, the bomb trigger also locked the door. By the time the gas started to leak out, all I could do was sneak out the vent I should have come in through, while the surviving hostages screamed at me to stay away from them before choking to death. Probably not going to get Secret Agent of the Year for that one,

The mission ends - some tough encounters later - in a confrontation with Zeke. He has a hostage, and you have a choice: talk him down, let him leave, or attack. Talking triggers the game's interesting conversational combat system: each tack you try gets a particular response from Zeke, and each of those has a right response, a wrong response, and one that will neither drive him over the edge nor calm him down. The exact lines Zeke throws at you are somewhat randomised, so you can't just memorise the correct responses to each, you have to think about what he's said and figure out the right counter-argument for his frame of mind.

I just punched him. A friend, playing for Edge magazine, punched the hostage instead - an innovative solution he didn't quite intend, but which nevertheless saved her life.

Human Revolution is a much tougher, harsher game than I imagined - even with augs you wouldn't normally have. It's visibly more futuristic than the first, the melee and cover are very different, and that first half hour is misleadingly straightforward. But none of these things stop the meat of the game from capturing the Deus Ex feel: thinking "OK, how do I want to play this?", stumbling across interesting alternate routes, and panicking when it all goes wrong.

Without that hard edge of difficulty, Human Revolution would miss the point. With it, it's a very exciting game.

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