This is really the only way for multiplayer to work in mass effect IMO. Well, you could have competitive objective type games I suppose. First yeam to kill a pre-determined number of enemies or something where the challenge isn't combat with the other team.
I digress. In regard to a gauntlet mode, it might be neccesary to restrict players to each having a different class. Three or more vanguards charging around the map would become a one-horse-show really fast. Forcing players to choose sperate classes, or randomize between waves, would compel players to use more teamwork.
Also, having specific enemies that can only be taken down by a specific attack type could work well. So, having an enemy that is immune to anything but tech attacks would mean the tech class player has to attack first in order to make it vulnerable. Better yet, have bosses that require
power combos and teamwork that cannot be acheived by one or two
players alone.
Anyway, those are my thoughts on the matter.