Jamaica: The Crew is a set of twenty characters, each with a special power, that add flavor to the game without any big changes in the rules. The characters may be hired when you're able to pay for the fee of a harbor, and they are "loaded" like any other resource, following the same rules.
You might find it enticing to add several characters to your boat — especially since most of them earn you additional gold at the end of the game — but with fewer holds dedicated to the regular resources, navigation becomes more dicey. All in all, more challenge, more silly fun, more Jamaica.