Despite its name, Assassin’s Creed has been more about the combat system rather than stealth. You are supposed to be a master assassin, someone who can use the environment to your advantage. Sure you had carts of hay to hide in before, but it was the countering mechanics introduced in the second game that really defined what people thought of the series.
Those aspects are still in the fourth game, but a greater range of stealth abilities have been crafted, allowing you to perform daring moves ever so quietly. Ubisoft has released a lengthy video walkthrough, only giving us a taste of what to expect when Black Flag hits current-gen, next-gen and PC platforms later in October.