We'll tell you this once: if you want to go into Bioware's trilogy finisher blind and save the surprises of the opening hour, then don't read this hands-on that covers just that.
The following deals with everything from the portent of doom that's the opening text crawl to a cliffhanger. We're going to pull our punches as best we can, but if you want out, now's the time to read something else on the site. For there be spoilers within.
We're plonked down in front of a HDTV, the end unit in a long line resting upon a table groaning from the weight of consoles, cables and screens. We studiously avoid glancing at the action on multiple screens as we pass on the march to our cubicle.
The demo is so long, press numbers so high and booths so few that a waiting list is drafted in order to get a free machine. Come the day's end we'll have clocked a two hour wait - half an hour longer than the demo's promised play time. No one minds.
Background chatter by the booths oscillates between the louder conversations of those waiting to play, and the hushed whispers of those that have. There's an odd charge to the atmosphere as excited gamers outweigh objective players. It pervades the skin then quickly dissipates as we sit down and strap in, powerful headphones dropping over our ears signal for exiting one world and flinging ourselves into another.
As we're offered the usual pre-game choices for the new player, there's a wistful thought that we could have brought our previous game save in. Background story, military type, whether we play for story or challenge. Choose those comrades fallen in the previous mission.
A few moments of instinctive clicking and a Earth-born Sentinel Shepard, with close bonds to fellow survivor Ashley strides through a busy corridor of military types.
He's being dragged into a council meeting to offer reason for the silence descending on colonies across the galaxy, a silence edging towards Earth. A silence shattered by a moment that you really wish you'd have witnessed in a cinema: the Reapers have found home.
The mechanical titans hammer through and the clouds and into the city around you, their bulks spearing the planet's flesh rolling out concussive shockwaves across the land. Buildings collapse, glass shatters, bones smash, flesh rips and burns, and the council is wiped out to a man. A brief look outside the window shows the same fate across every inch of the city.
Its a scene that's clearly War of the Worlds in conception, but no less impressive. We take several moments to absorb the destruction before joining a greying Admiral Anderson in a race down the building's exterior struts towards ground level and to radio in the Normandy, the sequence serving as tutorial for your moves, tackling Geth Husks swarming the buildings around you even as Reapers rip apart military cruisers in the skies above.
For all the horizon-scorching explosions, the devastation hits home by way of a quieter scene amid the carnage: a lone child hiding in a air vent of a partially destroyed flat. Despite Shepard's assurances (we choose not force the brat to haul ass out of there) the boy declines, knowing Shepard won't be able to help. Cue piano track designed to pick at the heartstrings. It's a meeting that'll come back to haunt you come the climax of this earth-side opener.
You leave Earth aboard the Normandy with the death toll rising and charged by Anderson to seek out a solution - and fast.
It leaves us in a quandary, and further inflames the burning question we've had about this climatic Mass Effect entry: how does a studio balance the diverse exploration that marked the first two games against the need to counteract the ongoing extinction of your home world as swiftly as possible? How can you enjoy a sprawling RPG when the opening arc dictates Earth's survival hinges on your actions?
The answer, or at least a teasing hint towards it, comes from the first main mission, as we land at a Mars Research Facility in search of a possible Prothean solution to the Reapers, only to discover the staff slain and the data wiped by Cerberus agents and a mysterious new antagonist who marks the demo's end with a brutal skull-crushing full stop.
It's a hefty and impressive first mission; the landing outside the structure letting you appreciate Mass Effect's visual enhancements, as the facility is shadowed by an inbound storm swallowing the horizon. Sand whips along the ground and billowing winds pull at crate tarpaulin so convincingly you're left entranced by the effect.
Once inside we get to grips with the squad-based combat system, sweeping and clearing our way through the various rooms, along tram lines and working out winning strategies for different foes: ranging from Let Ashley Do The Hard Work From a Distance, Use Singularity Every Time, and our personal favourite, Shotgun The Bastards Until Dead.
The last isn't really effective against shield-carrying foes, but we take a dark enjoyment from the realistic character animation as they're shoved backwards by the repeated blasts. Against Biotics the trusty blaster doesn't feel immensely futuristic, but it's damned satisfying.
Commanding the squad is, as expected, relatively painless, while the choices of attack are low at this stage. We only encounter one niggle as we try and position everyone ahead of a tram arrival to lay down flanking fire, as we're unable to highlight a choice spot behind crates on a overhead platform on the far side of the loading bay. It's a small issue that doesn't linger, and we're soon fully immersed into the gun-ho attitude of rolling lines of fire, coordinating attacks generating plenty of adrenaline. Even on normal difficulty, you've got generous dollops of health to allow for any tactical errors this early on in the game.
Our time with Mass Effect 3 ends with two notable moments. One is the reappearance of the Illusive Man, and after a brief argument over dominance of the galaxy, a mini-chase sequence as we try and stop his agent from leaving the surface. Success is blighted by horror in a sequence that proves this time round, nobody is safe.
But as the scene's cut short by a hovering Bioware representative turning off the Xbox 360, we're left with an impression that the story arc will, in part, form a galaxy-wide hunt and a resolution of lingering plot-lines. Galactic killing machines aside, we're left with proof that humanity's worst enemy is itself.
That a near ninety minute hands-on with the game's opening can be considered teaser just reassures that Mass Effect 3 has lost none of the franchise's length, even if the pace has been quickened considerably.
We sit for a few moments in reflection, only to be interrupted when a colleague bounds up eagerly to take over our spot. We stand, offer a quiet word of thanks to the staff for what we've played, and walk out. There's little more to be said: the end of the world is here, and it feels fine.