There's no a great deal of information released yet. As you can see from the trailer, the conflict that this story is centered around is the American Revolution. It sounds like a lot of the combat is being reworked to give a much more offensive feel to fighting, and it sounds like we are also going to get to effectively dual wield weapons (complete with dual counter attacks and the like). It also sounds like they will continue to support a multiplayer.

I don't know how reliable it is, but the Assassin's Creed wikia has referred to the new Assassin we play as "Conner".