This is the first game in the series where you can play as a Templar, the enemy of the Assassins. In the beginning of the game, Shay, your character, is an assassin, but gradually he realises that the assassins are trying to temper with the humanity and that's why he decides to fight them. The game has the same gameplay as AC Black Flag.
You get in the possession of a vessel that can be upgraded. Also, Shay can upgrade his gear and can buy and sell different things.
Upgrade Morrigan you vessel if you want to be successful while sailing the seas.
The game is short and it did not bring anything new in the series, but I liked it.