I've played this game last night. Visually stunning water detail, gunsmoke and amazing sunsets and great atmosphere. I dont know if this has already been mentioned but what would help immersion even more would be to include some sounds and visuals of wildlife. Seagulls and other large birds when you are near land and ports for instance; large fish, dophins and whales surfacing in the distance once in a seldom occasion; dark shapes in water, perhaps sharks circling crew members who fall into water during combat (if they do), or small flocks of birds that trail ships or sit on masts. I'm not saying it needs to be oversaturated with detail but it certainly could need some touches of it.
I hope that's in your cards, right? It would really make this game exceptional.