Ubi also showed off a bit of the mostly-co-op shooter's player vs. player action. It goes down in an area called the Dark Zone (imaginative), where you can find fancy loot if you venture in but run the risk of teamies betraying you, shooting your face off, and stealing your hard-stolen shinies. This one is going to ruin friendships, isn't it?
Here's a gameplay trailer which is clearly more scripted/practised action and dialogue from Ubisoft but does show sneaking and friend-murdering. Also fun, a bit of friend murder.
Or if you want a plain old E3 trailer, here's this one of those general-purpose doodads: