Well in fable 2 they have taken the every action has a consequence up again and this time they are serious about it, if you trash a small village/camp it will later on become ruins, if you on the other hand decides to help it, it can grow into a city. The co-op thing was something that was dropped in fable 1, and you find some traces of it in FE, the thing that is different with fable 2's co-op is: All the xp, money (maybe even items) gained in another players world, you can take home to your own world/singleplayer game. (you invite someone to your world and you play from the current point your character is in)
To me it sounded like this was a new way to mix singleplayer and multiplayer into one thing.