Mass Effect 3's best ending will be easier to obtain if you spend umpteen hours in multiplayer, raising your game's Galactic Readiness ahead of the final Reaper battle, but don't worry if you outright despise multiplayer. BioWare has come forward to clarify the mechanic, which modifies your vital Effective Military Strength total rather than adding to it.
Quick refresh for the late-comers: your job in Mass Effect 3 is to mooch around a war-troubled galaxy, approaching representatives of key races and factions and saying things like "hey kids, why not put aside your stupid centuries-old sectarian differences so we can all concentrate on giving Johnny Reaper a jolly good stuffing". Once they're on board, races and factions contribute their warriors, fleets and so forth to your War Assets total, which in turn feeds into your Effective Military Strength. The higher the EMS, the more likely you are to administer said jolly good stuffing.
"Focus on that bar," says Bioware's Jarett Lee (via Beefjack) "That is your indicator of how well you will do in the end-game." Your Galactic Readiness percentage greases the axles, but doesn't power the motor: it simply multiplies your EMS total, letting you short-cut the minimum number of War Assets required for victory. Get 100 per cent War Assets, and you needn't bother with multiplayer at all - especially as there are more War Assets available in the galaxy than are necessary for optimum campaign completion.
In summary: "EMS = success. EMS can be maximized via collecting war assets alone, even if your Galactic Readiness is 50%." Phew.
Hope that clears things up for you, Shepard. Mass Effect 3 is out tomorrow, and if you've read our review, you're probably on tenterhooks. Mind out if you're a returning player, though - the game has trouble importing Mass Effect 2 saves from cloud storage. Here are four Mass Effect 3 endings we hope never to uncover.