I would like to see more varience in terrain, as well as more geological features.
At the moment, the terrain we have is: Mud flat, Grassland, Heath, Moor, Connifer Forest, Broadleaf forest, 3 types of Swampland, Rivers, Lakes, Thicket, beach, and "Mountains" (which seem more like a big pile of rocks, nothing like a real mountain).
Of those, the Forests, Grassland, Moor, and Rivers seem to be the most useful, while Swamp, Mud flat, and Thicket are relatively useless, and in my exploration, Heath, Beach, and Thicket, are quite rare.
I'd like to see in the future; Jungle, sandy Deserts, Volcanic, Oasis, and Tropic terrains.
As for geographic features, I would like to see:
Real mountains, with a mix of rocky, mud flat, forest, and/or grassland terrains, grouped together to create a mountain range (which may even divide the map so only skilled explorers would be able to make it across to the other side until civilization creates a road to cross through).
Large Seas creating a divide between regions.
Landlocked Lakes and Ponds, to provide water resources (water and fish), to settlers in the middle of the forest/mountains, far from any rivers (for hermits who don't wish to locate themselves close to the much traversed waterways)
More Islands, in Lakes and Seas, large enough to accomidate a small settlement (but not so small they can only hold 1 house and some workspace). I've done a bit of exploring, and none of the lakes I've seen so far have any islands at all.
Frozen Tundra, during winter, or in the highest peaks of the mountains, ice and snow terrain, mixed with forest, rock and grassland terrains.
And
A Volcano surrounded by a charred Volcanic wasteland, complete with bubbling lava in the cone, hardened lava flows, and various interconnecting lava tubes.