I love Marshes and wish we got more out of them.

A lowly +1 Food makes them an overlooked early game boon. Compared to a Farm, they lack the 0.5 Housing but don’t require a Build Charge. They can receive +2 Production from the Lady of the Reeds & Marshes, +1 Production and +2 Science from Etemenanki, +1 Science from a Zoo, and Buildings in Districts built on Marsh by Vietnam receive +1 Production.

Theres not nearly as much as you can do with Marshes as you can with other features and they have fewer resource options. I would have liked to see more