If you haven't enjoyed or played the others in the series, don't let that deter you!
Picture Assassins Creed (stealthy & easy controls, beautiful scenery, assassin contracts) meets Far Cry (hunting, crafting), and TONS of ship battles, treasure hunts etc.
This time it's far less focus on you as a player roaming on foot/horse. At least half the game is played in the ship, which is AWESOME.
The sea is beautiful, and incredibly realistic. The storms are scary and intense. The ship battles are fun and deliver on the satisfaction you'd expect from crushing another ship in battle and taking their crew and cargo. A very welcome unexpected element was all the "pirate songs" you can collect and hear your crew singing. You can turn it off if you hate it, but I find myself whistling the tunes through out the day. They're pretty songs!
The only reason this doesn't get a 10 from me, is that it allows people to pay to skip ahead making it an unlevel playing field.
I have not yet played the multiplayer. I have heard it doesn't allow for ship battles and the such, but rather just a catch me if you can type of chase mode. If that is the case, it would be a huge let down, but the game stands on it's own as a single player in my opinion, as it has in the past with similar multiplayer modes.
This game has an intense amount of things to do. From sinking ships out in the open seas to plundering the depths of wreckage. Sure there is also the reoccuring assassins missions and eavesdropping. But its so much more than that now. And on the XBOX ONE, the water looks so real and its such a sight to see on a clear sunny day. At first though it can be quite overwhelming. I completed this game in its entirety in under 24 hours.