In the latest episode of BioWare Pulse, the new human-piloted mech called the Cerberus ATLAS Walker was detailed by Bioware lead animator Scott Mitchell. Shepard will first encounter the ATLAS manned by a Cerberus trooper, likely indoctrinated, and will be overwhelmed by its hulking power. But by damaging the mech enough and getting close to the hatch that opens, he (or she) can easily turn the tide in the party's favor.
From the move tree in the video, it seems as though the ATLAS will give Shepard the ability to ground smash, fire its heavy machine gun, rockets, smoke grenades, and perform what looks like to be a "2P Synch Grab". Not sure what that means - maybe it will pick up and hold one of your party members hostage - but it's going to hurt. Of course, once Shepard hops into the mech, there should be more than just owning Cerberus officers. Giant mech battles? I hope so.