Navigation at sea and boarding other ships that occupy much of the experience of the game are very innovative.
However this game is weak compared to other episodes; no real plot and gameplay that becomes (too) repetitive.
Many points on the map to explore, but many are as alike as two drops of water. The BO (background music and immersion) is not the strong point of the game either.
Some references still to Mayan temples and lavish decor ... It is a slap graphic, certainly. A good point. But Assassin's Creed II is for me the best episode from every point of view.
Overall, this is still a good game despite the need for greater diversity of visual styles and a BO a bit more interesting.