Yeah, so, as predicted after the three default campaigns available in the game have been completed, there's also going to be a fourth to follow en route thereafter starring Ada Wong. What is especially surprising, though, is that her story is apparently completely solo - no AI compatriots of any sort. Which is pretty neat, and again highly surprising given the increasing focus towards multiplayer gameplay the series has lead to.
And much like the other three, you can also ''meet up'' with other players as Ada's story clashes with another, e.g Leon & Helena's. We're (mostly) all aware of this aren't we? The whole mechanic where the stories will conflict and you can then join up with another two players to, for example, fight against a boss? Well, yeah, there's that.
What's more is that there's also this Agent Hunt mode, which is quite literally RE6's iteration on the Versus Mode from the Left4Dead series. Though it doesn't function quite the same, least I wouldn't imagine as such? I mean Left4Dead's Versus mode works because there's a lot of dynamic randomness to it, so just because you as a Tank dies only means that you can then respawn after a few seconds. A player taking up the role of Ustanak on the other hand, should that player die... err, what then? They're instead forced to just watch the rest of the chapter? It's all a little iffy and doesn't sound particularly balanced. Oh well, I imagine this is the ''competitive'' mode they've been hinting at, and rather something like this than another generic 5v5 series of deathmatch modes. I'd really want to see this mode in action for myself so as to get a better perspective on things, though.
Anywhoo there's now going to be four story campaigns in RE6. Of course this wealth of content won't matter if the gameplay is still kinda sucky, but later versions of the game look considerably more optimised. But anyway for a nut like myself, more RE story suits me fine.
EDIT: In true CAPCOM fashion, they're also open to showing a fair bit of what Ada's is like. It's meant to focus more so on puzzles and solitary combat, which honestly resembles the RE4 era of gameplay moreso than Leon's. A lot of dingy dungeons and the like as well, which is rocketing Ada's to look like the most appealing campaign of the lot. Though this being ''completely'' solo isn't the most suitable way to put it, what with the cross-campaign multiplayer looking to take a fair amount of time within the campaign.
EDIT2!: lol, oh, and here's some Agent Hunt gameplay... shit looks pretty terrible.