Surprisingly Good!
While its nothing mind blowingly innovative it was the perfect amount of old and new. Only a few issues. The same kill animations for the captains of ships get fairly old fairly quick, the absence of music in some parts make them slightly bland, the controls during the sneaking and treasure hunting could be slightly more refined.
If you want something quick to play then you can just go around attacking ships and gaining wealth. But if you want a deeper adventure then there is the story of finding your lost family, and hunting treasure. While there aren't many side quests that you can play, you can eventually remove certain powers from the game by attacking all their towns and putting in a new governor.
But on the whole it is a great adventure game that everyone with a PSP should get!