This one’s pretty straight-forward, but I think the “Water” category should be replaced with a “Natural” category. Having a “Natural” category would move the Grass, Ice, Mud, etc materials into a unique section.
This makes more sense than having Water have an entire category despite only having three materials imo.
On a lesser note, it would be nice to have more variety of grass available. In game there’s already a few grass varieties not available to the player, such as the Backyard of the Suite Condo. Also there’s a free collection of natural landscape materials on the UE4 Marketplace.