Everybody knows that pirates and ninja are mortal enemies, but apparently pirates and accidental Caribbean assassins go together a bit better. Black Flag moved us away from the story's roots a bit by throwing in a protagonist who didn't even intend to ever be an assassin and had no real knowledge of the war against the templars. He just found a cool outfit, put it on, and got down to the business of killing and looting!
The emphasis on ship combat is what entirely makes this game great (so something good finally came out of the maligned third installment, which first introduced the idea). Between the island exploration, tense naval battles, and typical city assassination elements, Black Flag is one of the most straight-up enjoyable entries in terms of game play.