Prepare to get engaged in the Caribbean!
After that, the game is very fun to play... you'll never stop having some accomplishment at hand so it is very hard to stop playing and between ship battles, treasure hunting and dancing with governor's doughters you'll find yourself spending a lot of time with this game.
One thing to keep in mind is the temporal nature of the game... you age over time and if you spend too much time on side quests, you'll end up being a great pirate but your family will have to remain in prison... which is not the idea... so, is up to you to find a balance between making money, finding treasure, doing trades and (remember) findind your family.
Enjoy this game....