The open world is not as fun as it could be due to the lack of valuable traffic/variety. If people's deliveries & captured goods were shipped in the open world there'd be more targets to accost/defend/raise hostility, and the world would seem more vibrant.
Being a pirate is not fun, see above, and since pirate's can't attack pirates, but we have a home port, we're like a bad nation, not an individual sneaking about, using our wits and fame to turn a fortune. I'd like to see more of a privateer role, false flags, pirate ports done away with forcing us into free ports only, and let pirates attack pirates. If you want to be a pirate you better get used to the entire world being against you.
The process of joining a battle is not fun, right now it feels like you're locked in an imaginary room with someone. No dramatic rescues, no helping a friend who was just in sight a second ago, no one joining late forcing you to leave your prey. If we figured out a way to make battles less obvious in the open world (only play cannon sounds, show smoke or something when you're close, or only show the icon when you're really close) but leave the battles open, the open world and battles will seem more tightly coupled and less like you're jumping into a locked session that can't be tampered with. DO NOT underestimate the effects of feeling like all is lost because no one will save you OR OMG my friend is here, so glad you showed up.