Well, you asked about changes, yet there are a lot, so I'll simply post the highlights:
There's more ships ~ these are in multiple variants through all the game levels. There has been an increase to the variation to ship outfittings after a major re-balancing of them took place. All items in-game now gradually increase in potency as you level for the ship size you're using.
More content ~ both in terms of the lvl 50 epic group missions and also in-terms of revamped existing missions including xp increases to bring them in line with general Open Sea ship hunting. Daily missions that you could take for different numbers of players in a group were also introduced in the last patch. Luxury clothing was added that you can purchase at your nations capital from the tailor shop in the auction house. There's also titles that you can now give to your character also, which you get from completing certain missions, killing a number of your enemies in pvp to your prowess in the game economy!
More in-depth pvp ~ all nations can enter a single battle, not just 1 nation against another. There's reinforcements, which means a player being ganked can have up to 9 friends join in the battle from reinforce points within the instance. There's also new group mission content to help assist in generating positive or negative contention on a port.
New Town Renders ~ completely new colour pallet for all towns, many of the significant ports (Tortuga for example) are now massive tier towns, with many twists and turns resulting in lots of places to explore
New Tutorials ~ a complete re-vamp of these took place, including UI changes to make it easier to go through the tutorial for the first time. Every Nation now has it's own tutorial type.
Mission Helper ~ Points out key missions for your character that you've missed during your travels
Compatability ~ something that wasn't available at launch, the ability to play this on a system that used certain intel chipsets, fixed that.
This is all on top of countless bug fixes that have taken place since launch. I agree entirely with what Arkiya stated, the game in itself was pushed out too early, the game as it is now is a lot more polished, not just in terms of content but also in terms of the feel of the game in itself. There's very little lag within the game now, thanks to coding changes that took place 2 months back.
So yeah, it's all well and good me writing this stuff but if you'd played it before or even if you haven't, this is becoming a very complete game. So feel free to come give the game a try!
You'll find this information is placed here too Asna because, although the game is under complete control of Flying Labs Software in terms of how the game is designed, it is published by SOE (or how they're known in this context, Platform Publishing).
Oh I almost forgot! If you get in this week, you can take part in the celebrations for International Talk Like a Pirate Day! There's missions in-game vary from teaching some poor excuse of a pirate to go YAAAR! to getting a parrot (who enjoys rum a touch too much) to say "Shiver me timbers!" There's exclusive items available to celebrate including a certain ill-tempered, foul-talkin' parrot!
YAAAAAARR!!!
With a Station Pass I would hope.