why assassinscreed, black flag is considered as the goat? so much water

I love Assassin Creed.. specially when I get to explore a lot of ancient places, monuments, see different people from that era, their dresses, culture and all that.. I just don’t understand why black flag is considered such a good game when it’s mostly a ship which you need to sail around and see dolphins swimming around. I don’t get it…
so I just want to know some really honest feedback, why do you guys love black flag so much?