One of the most dynamic games I've ever played - Shoot a fellow pirate's ship and you could start a war, start an ironmonger, and the cannonballs you make could end up blowing holes in your ship. Lose at poker, and that money could go towards your enemy's funds for blockading your island. Everything you do can (and will) have an impact on the world.
There's a real sense of achievement when you continue the game - you start as a pirate with a bandana, a few clothes, a flimsy foil sword, and you can end up the ruler of an island in a month. There's no real skill level grinding, due to the rating system that rewards natural puzzling skill. The game is fuelled by it's vibrant system of crews and flags, supported by the sense of close community - after all, you can't sail a big ship on your own. The economy is fairly deep, and it is nearly entirely ran by the people who play the game. Need some sugar cane for your distillery? Order it from an island and ship it in, or wait for someone to do it for you.
The game is filled with colour, and the cartoon design adds a nice friendly touch, the games are addictive and fairly plentiful. The range of things you can do as a pirate is massive once you get in to it. A really fun and addictive game. :)