Journey and Resident Evil 6 couldn't be any more different, but the latter is borrowing a major idea from the former and games like Demon's Souls: their multiplayer functionality. Capcom calls it crossover gameplay, but it breaks down like this: There are three pairs of characters in Resident Evil 6--Jake and Sherry, Chris and Piers, and Leon and Helena. At various points in the game, these characters cross paths for both narrative and gameplay purposes. Much like in Journey and Demon's Souls, if Resident Evil 6 knows that your friends (or strangers, if you select that option) are at a point in the game that would put them on the corresponding "opposite" side of your current game, they will automatically join in and take control of the other characters. The new four-player team can then coordinate via prefabricated AI commands or through voice chat, and though Capcom said it isn't currently working, the plan is to make these kinds of multiplayer matches support four-player voice chat.
It's an interesting feature that should prove itself useful in boss battles, particularly the new encounter we saw during the show that featured a grotesque, mutated creature named Ustanak. Aside from his hulking size and powerful mechanical arm, Ustanak can pick up individual players and place them in a cage on his back, forcing other players to coordinate attacks to free their imprisoned comrade. Working as a team also makes it possible to distract Ustanak so that other players can move around the area and make use of environmental objects that might aid in the battle.
We didn't see what happened at the end of this battle, so it's hard to say how much time you'll be spending with another pair of players, but it seems all but certain that cooperative boss battles are a major part of Resident Evil 6's multiplayer.