I played with the base game and with the expansion separately, to see whether or not I thought the expansion was good, and frankly - it is. The expansion has two things going for it:
One is that it lets you play with 3 more players, increasing the possible player count to 9, which is a great number for a party game. The alternative is buying two copies of the base game, which would cost you about $5 more and nets you one more player (10 players total if you get two base games). So it's a value expansion on that aspect.
The other thing going for it is the mechanics it adds, which specifically are the parrot and monkey cards. The base game's wild cards are the bomb cards which turns one of your ships into a trap. This expansion adds monkeys which are like that mechancic but even more lethal. Rather than blowing up both ships, you can give your opponent -5 treasure instead, (or up to -8 if you have one of the new captain cards in play). Then there are the parrot cards which I think add tons of depth. You basically copy the stats of the front of the ship, so you can strategize what you want to reveal even more.
The game added some extra depth that is appreciated. It makes the game like 1% more complicated, but you get little cheat sheets that you can remind yourself how the monkeys and parrots work, so it kind of counteracts that.
Overall, it's definetly worth it on the player count addition alone, but the extra parrots and monkey cards add way more enjoyment to the game, so it'd say it's a staple expansion. Also you can actually play this expansion standalone for up to 3 players. The box is the size of a deck of cards, so you could just put this game in your pocket as a "just in case" game for a hang out for up to 3 people.
I'd reccomend this for sure 10/10