The picture above, snapped by Joystiq's Mike Schramm at SDCC, is the only clue BioWare gave during its panel of what's next for Mass Effect 3. It clearly shows a Cerberus Atlas mech, but what is that environment? Could it possibly be an underwater landscape? Something to do with Leviathan, perhaps?
Earth is burning. Striking from beyond known space, a race of terrifying machines have begun their destruction of the human race. As Commander Shepard, an Alliance Marine, your only hope for saving mankind is to rally the civilizations of the galaxy and launch one final mission to take back the Earth.