The basic idea is that a team of 12 guardians have to last as long as possible against an onslaught of the enemy army(there will be a different one per faction). It's meant to replicate what it would be like if the Tower Vanguard went "-blam!- it, send as many guardians as we can to kill EVERYTHING" Of course Vehicles and turrets will be available, occasionally an enemy will spawn that activates the "Boundless Light" buff. And imagine all that sweet sweet loot. Periodically the enemy will send out their biggest heavy hitter and if you manage to defeat them you are given the option to take the rewards you've thus far earned and go home, Or keep fighting until no one is left standing. Edit1- A better POE... Essentially endless, wide open areas with plenty of different vantage points and cover locations. I imagine the arenas being about the size of the Cosmodrome with less geometry separating it's various sections. Maybe like the size of a BattleField Map? Edit2- You know the first destiny live action trailer? You know that opening bit where there are thousands of thrall running at the guardians? Yea that's what I'm imagining.