It has elements of POTBS in both design (from what we know) and gameplay, think POTBS slowed down with no skills, manual aiming, and manual sailing. It really captures you and gives you the same feeling of excitement in a large battle.
How the open world will compare is unknown as a whole, but if you liked POTBS there is a good chance you will like this game as long as you weren't a die hard fan of 'magic' skills.