Here's my comments on the uniques/abilities:
Grote Rivieren-building campuses, theater squares and industrial zones next to a river awards major adjacency bonuses, completing a Harbor grabs/culture bombs adjacent available tiles.
Another Civ ability involving adjacency to a natural feature
, I guess the Netherlands won't do too well if their land is devoid of rivers. The culture bomb ability seems weaker than the other Civs with that, since it would be mainly grabbing water tiles. Ability seems to be reference to the Netherlands' many rivers. I was expecting something to do with trade, but oh wells.
Radio Oranje-your trade routes to your own cities provide +1 Identity per turn to the starting city, Trade Routes to foreign cities or from foreign cities provide +1 Culture to you
Since, I'm not too familiar with how they are doing Loyalty, I'm not sure if this ability is strong. Presumably this Identity has to do with keeping loyalty in your cities. Is Foreign Cities providing culture is a reference to something specific?
De Zeven Provincien-increased ranged and combat strength, receives additional bonus when attacking defensible districts
As expected, the Dutch receive a naval unit. It seems useful on Island Plates maps.
Polder-Unique improvement built on water tiles with sufficient adjacent coastline, provides food, production and a bit of housing, gain additional bonuses with later Civics and technologies.
The most interesting aspect of Civ6's Dutch Civ to me. Seems pretty powerful and will match the Kampungs of Indonesian. I wonder how much is sufficient adjacent coastline?
Anyone recognize the Dutch theme music?