Heres a brief list of all the things that i think should be in a decent multi player pirate game.

SHIPS!!!!

- these should be the cornerstone of the game. But it would be good that if rather than having rigidly defined classes of ships that limit the capacity and whatnot, it would be nice to have a continuum of ships. So a ship would be defined by its capacity resistance to water amount of sail turning circle etc.

Cannons

Big cannons, little cannons, broadsides ranges, swivel guns, bow chasers, stern chasers, cannonades, cannonets, round shot, chain shot, stone shot, red hot shot, mortars, exploding shells and of course grape shot. not forgetting muskets blunderbusses cutlasses and grenades.

PIRATES!!!

- yarrrrr, but also traders, navy, smugglers, privateers, whalers and all sorts of other reprehensible swabs!
These again should not be rigidly defined - no you're playing as a naval officer so it works like this .. etc - your actions should define what you are perceived as.

PORTS

- Pirate ports, trading ports, naval ports, heavily armed ports, careening beaches and hidden islands shaped like giant monkeys.

You should be able to interact with ports buy sell repair attack pillage and take over. Possibly at a later date even discard your ship in favour of running one.

Naval Battles

What the majority of the game should be about - tacking and firing canon, taking damage and boarding actions. It would be nice to be able to group and load different cannons with different ammo andfire them at diffeent parts of the oppositions ship with differnt keys. like the ubit groupings in command and conquer.

Commodities

Food

Drink

Treasure

Weapons

Raw Materials

Luxuries