Mass Effect 3 preview

At the centre of the roleplaying petri dish, a colourful swirl of games are gently bleeding into each other. Flat-out action games adopt the character builds and XP systems of the traditional RPG, while roleplaying adventures of a certain mass-market mindset bury their statistics deep behind rows of headshots.

Mass Effect 3 looks to be a high point of this trend. BioWare say that it's set to make a leap in quality beyond ME2 like the leap ME2 made beyond the original.

Eager to temporarily borrow the keys to someone else's Shepard, deep within BioWare HQ I saw off enough Cerberus commandos to give this bold claim credence. The premise of my early mission was a violent race in the shadow of an encroaching sandstorm through a Mars mining facility.

A Prothean artefact with anti-Reaper qualities has been uncovered, and both Shepard and the Illusive Man gang dearly want it on their mantelpiece. Aided and abetted by new boy James Vega (heavily inspired by Sawyer from Lost) and whoever survived from the Ashley/Kaiden collective in Mass Effect, the advance in action quality is apparent from the off.

BioWare have doubled the number of developers giving life to Shepard's freeflowing ducks, rolls, melee swipes, running jumps and potshots, and also to the combat smarts of the Cerberus and Reaper fodder that stand in her (or his) way. Shieldwielding enemies scuttle down parallel corridors to flank you while their buddies tactically retreat further up in the map, while the simple addition of verticality (ladders!) manages to spruce up level design no end. Sudden twists in the action were used sparingly in ME2, yet here they're laid end to end. Ambushes on incoming NPCs, surprise attacks from the dark through satisfyingly smashable windows, long-distance fire-fights on a moving monorail... there's more life on the Red Planet than you might expect.

The primary draw of ME3, however, is its role as a grand finale – a blaze of glory for your own personal Shepard. It begins with a hastily convened meeting between Shepard, Anderson and the woefully prepared leaders of Earth on the day the Reapers (the caretakers of the galaxy, who sweep up all organic life every 50,000 years) finally make their eventful return.

The skies outside the window are suddenly pierced by vast Reapers descending like clawed fists, who go on to stomp between futuro-Vancouver's skyscrapers and destroy all that stands in their path with unworldly 'phftang!' noises. Before anyone has time to comment on the scene's War of the Worlds feel, the room is awash with blood, flames and broken glass. Shepard's quest to unite the disparate races of the galaxy against their common enemy has begun.

If you're a returning hero, then your reputation and prior activities in the galaxy will take its toll on your recruitment drive. Gazing into the development toolkit of lead writer Mac Walters – a busy nest of stored decisions feeding into a mesh of dialogue possibilities – feels a little like being in freefall. “It took three months at the beginning of this project to deal with the decision to kill off any of the henchmen at the end of ME2,” he mutters. “They're all major characters, but they all could be dead. What were we thinking?”

The first game's binary choice of whether you save Kaiden or Ashley means you'll have either the sensitive soldier or the brunette space racist onboard (both suspicious of Shepard's dealings with Cerberus in ME2) but previous decisions made over the Rachni queen, the Collector base, the Genophage, the Geth and good old Wrex will also come back to alternately haunt or help you. Getting a perfect playthrough and appeasing enough alien races is promised to be very tricky indeed.

Enter stage left Mass Effect's controversial Galaxy at War system, a sort of social metagame hub where your success in ME3's horde-based co-op multiplayer (and the Facebook games and apps) serves as a multiplier to your proficiency against the Reapers on the approach to the endgame. You're presented with the forces you've amassed, including characters such as Samara and contingents of Asari Commandos and Mindbenders, and encouraged to shuttle them between Reaper troublespots. It's a needless addition, but a forgivable one if it turns out to be fun. Shepard's adventures tend to consume body and soul, so being able to aid the war effort while on the bus has a certain allure.

Inside and out, Mass Effect 3 is laced with feelings of wartime chaos. As I stood in the BioWare writers' room I couldn't help but notice stirring Churchill quotations pinned above the door. Anything in the game that lacked urgency has been trimmed (goodbye mining), and wherever you fly you'll see charred space detritus or fleets of doomed warships. The final battle will soon be upon us, and the bodycount will be high. How high? That's down to you.