Things are moving very quickly now that Mass Effect 3's multiplayer mode has been formally confirmed. BioWare only made it official yesterday, and now details from OXM's upcoming coverage of the mode have already slipped out (via Stick Skills).
Multiplayer in Mass Effect 3 will be realized as a four-player wave-based survival mode. Players will create characters, with control over things like gender, race, character class and, on a match-by-match basis, equipment loadouts. As you complete various 11-wave showdowns you'll earn experience that levels up your classes persistently.
Interestingly, multiplayer has been a planned feature of the Mass Effect series since the first game, but director Casey Hudson didn't feel comfortable bringing it in until now. This likely has to do with the galaxy-wide war the story is speeding toward, with the multiplayer directly tying into it and the single-player story by way of the Galaxy at War mode.
It seems that "War Assets" will serve as a form of currency in the single-player story to pay for the looming conflict. Players will be able to earn War Assets in multiplayer by completing missions and side objectives, which include tasks like hacking terminals and collecting data packets.
There's more to be revealed, both from the bullet points and in OXM's eventual preview, which will certainly clarify a lot of the less clear bits you've read. This includes a few "big" details that Stick Skills left out intentionally (and good for them for doing it). So be sure to check out the December issue when it hits newsstands.
Source: Stick Skills