Port Royale 2 is a pretty flexible game. One hand it's like a tycoon game. You setup trade route and production type. You own farm or factory and then sell the production to make profit. Or you can have your own town and build it to a florishing cities. THe economic system is rather on supply demand basis. It's pretty easy to follow if you think about the products logically. A city with garmet production will constantly have abundant supplies on garmet (so lower prices), but then demand a lot of cotton and thus your can make profit by selling cotton in that city.
Or you can approach the game in military way. You obtain letter of marque and destroy other nations military convoy to weaken them. And then you attack the city to conquer. Playing method will be pretty similar to Pirate! in this gameplay.
Or you become a pirate. I've never tried this, but it seems that only after you make deal with pirates in the inn, you can set foot on pirate stronghold. You will set up pirates network and get percentage loot from other pirates that use your convoy.
It is very hard to approach the game in military and tycoon method at the same time because once you organize a strong fleet, you will have at very high cost that is impossible to cover using an even profitable trade route. This is because you need to maintain the ships cost, crew cost and captain cost, which can only covered by looting other military ships and then sell them in the shipyard. More over, once you wage war to a nation, you can't trade with that nation for quite some time making your market smaller.
It has treasure searching mechanism as well, but rather brief as all treasures are floating on the sea. SO don't bother to look for treasure on the land.
THe battle is sometime annoying because you mostly have to use one ship against five. So you usually have to sustain a high damage for you first ship, but you can capture the enemy convoy in your second to third round.
Fun level is not too great though. Pirates! is more fun because it looks more like a children version of Port Royale.