Even though Big Ben's Clock Tower was the scene of the very first Mass Effect 3 teaser, when the Reapers start dropping to Earth next March it'll be in Vancouver - not London - that Shepard makes his stand.
Our fallen hero (now dishonourably relieved of his Commander title after Mass Effect 2's events) is in the Alliance's Canadian HQ when the alien invasion starts, and within seconds he's called up for advice and help. Not that it's any use to the higher-ups: those poor fools are promptly evaporated in front of Shepard's eyes by a Reaper laser beam...
Out for revenge, Shepard scoops up a handgun and starts battling back against familiar husks and cannibals, with newer Reaper-mutated alien races promised later on. BioWare are boldly claiming that the leap in quality between Mass Effect 2 and 3 is as significant as that between 1 and 2, and within five minutes of game time it's clear they're talking sense.
So much so that they could comfortably have stripped out the RPG elements and released this as an all-out action game. Shepard is much lighter on his feet and thinks nothing of sprinting across skyscraper ledges and leaping over gaps at the press of a button. Combat rolls, hopping over cover, melee executions from behind cover (thanks to a yank and a vicious neck stab) and SWAT turns are all part of a day's work in Shepard's new life. During the acrobatic display he even finds time for a spot of surfing, albeit down a collapsing rooftop as the cityscapes are reduced to rubble by the Reapers. It's new territory for Mass Effect, and we love it.
After 20 minutes of playing Earth Defence Force the Normandy swoops in and picks up our boy Shep. To hammer home the struggle facing the planet, the camera cuts away to a small boy we tried to coax out of an air duct earlier. He climbs into a transport carrier and is whisked to safety - safety that lasts all of three seconds before the vehicle's reduced to a smouldering wreck by another Reaper laser.
Suitably motivated and sharply reinstated to Commander status by Admiral Anderson, we head straight to Mars to skim Prothean data to try and find a means to fight back.
Mars is just as hostile, but for different reasons. While the Reapers are concerning themselves with Earth, the Martian researchers are being executed one-by-one by former 'allies' Cerberus. The bad-guys-turned-good are back in full-on bad mode now, partly because they want to use the Prothean technology to control the Reapers rather than destroy them, and partly because of a spoilerific reason too juicy to reveal.
And it turns out that Shepard's not the only one who has brushed up on his combat skills since the last game. Enemies do everything they can to force you out of cover, and love nothing more than chucking grenades (regular grenades too, not the floating discs of old) and flanking to catch you unawares.
Cover-to-cover hopping is the only way to survive, and even then victory isn't assured as cartwheeling Phantoms and hulking mechs make you squeeze every last drop of tactical nous out of your squad to survive.
As the Mars level continues it's obvious Mass Effect 3 is doing things we'd only dreamed of before. Modular armour and customizable weapons ramp up the options, while experience is scooped up thick and fast during combat and goes towards a deeper character progression system with much more in the way of upgrade options.