The game continues Desmond's saga, who now plays the role of Connor, a native American in the 1770's. Connor must save the indigenous people and defeat the Templars as well. One of the heads of the Templars is his own father, and that makes thinks interesting.
You have the opportunity to participate in America's struggle for independence and get to know so many historical figures.
You have almost the same game-play as in the other games, yet now you can use fire weapons. There are so many side quests and so different enemies that you have to approach differently.
Overall it's a nice game with fantastic graphics. As I mentioned before I couldn't finish it (I was starting the 11th sequence when my save games were deleted).
I replayed the game from the beginning and all I can say it's worth playing.