By the end of BioWare's first Mass Effect game, regardless of the gender, facial features, moral alignment and sexual predilections of your own personal Commander Shepard (ours was a half-hearted moral fence-sitter with a tendency to try and screw anything that moved, despite the fact that he looked like an ageing sixth-form college lecturer), they were blasting into space as a fully-fledged Spectre agent, ready to kick off some serious intergalactic shenanigans. They were a pretty big wheel down at the cracker factory, in other words, but sometime soon after that - according to the sequel's enigmatic announcement trailer, at least - they promptly dropped dead.

Or did they? The answer to that one's a little bit confusing. BioWare used an E3 developer presentation to reveal that Shepard's definitely who you'll be playing as in Mass Effect 2, but they also wrapped things up by showing us his death - or at least one of them. Twisting through space as the Normandy explodes in the distance, Shepard's grappling with his punctured spacesuit as he's dragged down into a nearby planet's atmosphere. Things look bad, then, and it's his own stupid fault, too, having been given a choice to flee in a cosy shuttlepod or stay behind to aid in the evacuation as his ship is lanced apart from above. It's the sort of decision that, for a player character, almost always leads to a glorious last-minute rescue in videogames - a fake-out and a rousing hurrah as you cheerily wobble back from the edge of the impossible. But here there is no rescue, and not much wobbling, except if you count your lower lip: Shepard falls and struggles and then dies. The end.

It's one potential death out of many, apparently: deadly treats liberally sprinkled throughout the campaign, all of them much more than a simple 'game over' screen and option to restart, each one an elaborate cinematic and a strangely satisfying conclusion. So, to recap, Shepard isn't dead yet, but you'll have to work extra hard throughout Mass Effect 2 to keep him alive - and you'll be doing that in a game which the developer is promising will be a lot darker and meaner, and a lot more refined, than the first outing.

Having taken on giant sentient spaceships bent on wiping out the galaxy on your last mission, for Mass Effect 2, things are a little more personal. All around the galaxy, humans are disappearing, and Shepard wants to know why, even if the answer is that they've just popped down to Bluewater for the afternoon to pick up some Crocs. They haven't, of course - everyone in the future wears Converse sandals - and Shepard soon finds himself joining up with the shadowy Cerberus organisation to dig a little deeper, and heading off on a suicide mission.

To do that, he'll need to gather together a gang of intergalactic hard nuts to race about the galaxy, occasionally riding around in a cheeky little tank and handing out brutal justice and vague, inter-species sexy-times. A noble venture, and one that our E3 demo illustrated by sending him into a glossy skyscraper city to track down a fishy-faced chap named Thane, who just happens to be the galaxy's greatest killer - outside of unattended step-ladders, naturally.

BioWare has seized the chance to fix a few of the tingling annoyances with the original game. The inventory and item-management system has been completely redesigned, apparently, although it isn't ready to be shown yet, and the comically slow elevators of the first title have been replaced with fancy neon-wireframe animations of you zipping from one location to the next - a dashing bit of misdirection, perhaps, but one that now covers some significantly faster loading.

More importantly, the dialogue system has been tweaked. Conversations and choices are now integrated much more smoothly into the shockingly stylish cinematics, and the butting-in system that was hinted at but never delivered in the first Mass Effect has been implemented, an occasional option to cut someone short now available whenever a left trigger symbol pops up. It works wonders in terms of making the exposition edgier and more natural, but be careful wielding your new powers of interjection: sometimes you'll find yourself racing in with nothing but a snide rebuttal, but on one occasion in the demo, Shepard ends a chat by pushing his conversation partner out of a skyscraper window.

Fighting has also been ever so gently retooled. The power wheel is still in place for selecting guns and biotic attacks, but you'll no longer need to pause the action to make selections. Weapons have been bolstered with nine new classes, including heavy options like a chunky new homing rocket launcher, and there's a raft of new biotics, all of which play on the improved physics engine, which sees the demo battle, taking place on the roof of a giant skyscraper, playing out in an impromptu pinball session of explosions, forcefields and cart-wheeling corpses. Team tactics are now contextual - point one of your squad at an enemy or cover and they'll know what to do - and there's a new body-part hit-detection system too, which allows you to take a robot's head off in a shower of sparks, or cut someone's legs out from under them.

Finally, the exploration element has been filled out. The galaxy no longer closes for business when the shutters of the story come down, and you'll have an added impetus to explore this time around. Along with scanning planets manually for a landing spot by moving a cursor over the surface, BioWare promises you'll also be visiting a greater variety of worlds, suggesting that you won't spend a lot of your free time touching down on a succession of differently coloured ashtrays.

With the rough edges knocked off the mechanics, and a lot more skill on display at handling conversations and framing the action, Mass Effect 2 seems to be balancing refinement with continuity as it heads to release. BioWare feels that even if you didn't play through the first game, this is still an ideal jumping in point, but more exciting is the fact that seasoned travellers can import their old saves wholesale, leaping into a narrative that acknowledges and incorporates every moral decision, every team-member death, and every unplanned burst of casual sex. Of course, that may mean you're stuck exploring the stars for a second time with a face like an ageing sixth-form college lecturer, but at least you've only got yourself to blame for that, eh?