Excellent Game
I can't believe there are so few reviews for this game. I guess everyone is busy playing it. I would suggest upgrading your ship with wartime features (not sails and ornate wheels) before you go too far into the story progress.
I still love AC Brotherhood the best but AC4 really was incredibly well done; The story line and settings are fantastic; You live the life of a pirate properly and travel from island to island with many missions for lots of gameplay hours.
The legendary ships are way too hard and I only got one of them using a cheat I saw on youtube; There was a real lack of community challenges for a while and you need them to gain certain items in the captains cabin; Occasionally some glitching and the game froze.