The next Spider-Man adventure will see Amazing Spider-Man and Spider-Man 2099 working together through time in order to fix a timestream gone awry. When Spider-Man 2099 is fighting an evil scientist, the madman somehow gets sent back through time where he proceeds to ensure a better and brighter future for himself. As a result, the future of New York is completely changed and no one knows any better except for Spider-Man 2099.
Spider-Man 2099 figures out a way to telepathically communicate with Amazing Spider-Man through time and convinces him that the life he is living isn't right. Not only is the perfect life that Peter Parker living wrong, but he's set to meet his end very soon.
Spider-Man: Edge of Time (All major platforms)
As we found out when the game was announced, the big "catch" of Edge of Time is the "cause-and-effect" gameplay mechanic. Amazing Spider-Man's actions will have a direct effect on 2099's world and the environment will change around you in real time.
In the section Beenox showed me, the two Spideys are in the same building (in their respective time lines) and Spider-Man 2099 is getting his ass handed to him in a fight with a giant robot. In Amazing Spider-Man's timeline the first giant robot prototype was still in development, so he has to destroy the robot before 2099 is killed. Once the robot is destroyed in the that timeline, the robot in the future timeline disappears and is replaced by several human-sized robots that 2099 has to fight.
Later in the demo, when you're playing as 2099, rooms will transform right before your eyes revealing new areas to explore and threats -- it's like real-time Day of the Tentacle. For all of the major events, the cause-and-effect elements are scripted. Beenox says that there are little things the players will be able to do to create changes, though. My guess is that it'll be something like finding secret rooms and items to help upgrade abilities.
At the start of the game, Amazing doesn't really trust 2099 at all. Who can blame him though? I'd be pissed off too if a voice in my head is suddenly telling me everything about my life is wrong and I'm about to die. So there's trust issues and the voice acting by Josh Keaton (Amazing) and Chris Barnes (2099) portray the frustration of both characters splendidly. Yes, Neil Patrick Harris won't be reprising his role and shamelessly stealing a voice acting award.
When the two Spideys are talking to each other, you'll see whoever is not being controlled at the time on the bottom-right of your screen. You'll actually see Spider-Man fighting and doing his own thing while you're playing with the other. Think of it like a picture-in-picture feature in TVs. The game seamlessly switches between the past and the future gameplay. For example, in the cause-and-effect example I gave, the player switches over to 2099's timeline once the giant robot was destroyed.
As for the core gameplay, it's largely similar to that of Shattered Dimensions. You swing, you punch, you web and there's plenty of smart ass remarks from the two wallcrawlers. Amazing has a new "evade" move that allows him to dodge attacks and 2099 can produce a holographic image of himself that will distract enemies. You can upgrade both Spider-Mans' skills and it'll be largely similar to the Shattered Dimension system. Other than that, you can forget the first-person fist fights, which is for the best as that feature in Shattered Dimensions was very out of place.
The end of the demo sees 2099 take a shortcut down an elevator shaft where you'll spend a good five minutes maneuvering 2099 through gaps and openings down the shaft, much like the free falling sections in God of War III.
Activision and Beenox weren't ready to tell us anything about Edge of Time's villains (they wouldn't even mention the scientist's name) but we can expect villains that haven't appeared in games before. The overall theme of the game has a very dark feeling to it too, as evidence by how Spider-Man 2099 is carrying a dead Amazing Spider-Man with his costume thrown to pieces at the start screen.
Did you like Shattered Dimensions? Well, then you'll like Edge of Time. The game was developed during the production of Beenox's last Spider-Man game and this is considered to be a standalone entry to the Spider-Man universe. Technically, yes, Amazing and 2099 are from different dimensions. Nothing with time travel ever makes sense and at the very least, Peter David (co-creator of Spider-Man 2099 and narrative lead of Edge of Time) will make up something to explain things.