Pearlbrook comes with a Riverside addition to the main board on which some new things happen.
There are pearls, a new way to pay in this world of critters. Pearls can be used to pay new wonders with, to play endornment cards and as 2 victory points each at end game scoring.
The new wonders take the place of the old wonders and they are worth (a lot) more points. They are also somewhat more expensive to buy and always require a pearl.
At the start of the game players receive two endornment cards. These cards cost one pearl to use and give you a one time bonus plus a scoring condition for the end.
Pearls can be obtained by placing a frog ambassador on one of the four spots by the riverside of there is still a pearl on a facedown card. By doing so, this card will be flipped and if the player can and wants to meet the conditions they may do so. If all cards are face up, players can use the ability of the faceup cards, which often give you a pearl, or use the top spot on the board, where two resources and two cards can be exchanged for a pearl.
I think the base game of Everdell is already a very good game that doesn't really 'needs' expansions. The game on itself doesn't need a fix or anything in my view. Having said that, Pearlbrook adds a lot of newness to the game that was very welcome for me, having played the base game to bits 😉.
The addition of the pearls feels fresh and new and gives the game a different feel to it. The new cards in the game look great and really work around the pearl economy. The river destination cards I think are very well designed together with the frog ambassador (love the meeple!).
All in all, I'm very happy with this expansion and if you are a big Everdell fan looking to expand your world, this is a wonderful expansion.