The first machine has basic prizes and you can only bet on one line, you use doubloons for each spin. The upper one has much better prizes and you play with pearls which you collect in the other machine. The possibility of winning is alot higher as you can bet on more lines.
The four mini games include: Rum’s Challenge, Naval Battle, Treasure Hunt and Dices. They are mainly slot machine based, so you have to spin and hope you get lucky. The mini games are activated by certain symbols. Collecting shovels and extra crew in your normal game play will make some mini games easier to complete. The prize in most of them is additional doubloons but you can lose them as well. The animations are very basic, but you don't really need them.
You as a Pirate age through out the game as well, which means the game has an ending and a goal. Leader boards are in Open Feint and there is plenty of achievements to earn.
It is very easy to learn how to play, and it looks and sounds great. Definitely worth a try!