When I first start playing an Assassin's Creed game, I'm not particularly inclined to understand the small intricacies littering city streets or guard AI. I do something nefarious, guards chase me. There's not a lot to it.
It seems like Assassin's Creed III tries to change that malaise and boredom by forcing players to react to the world, while the world is reacting to the player. Running away from a pack of guards in the wild? Better beware the thick packs of snow that can inhibit your momentum.
Trying to sneak up on a guard in the heart of Boston's port? Better take advantage of the new stalking zones. Are two guards approaching armed to the teeth? Fuck it, just hack them both with your tomahawk or hidden blade. Some things never change.