I don't use the ground very much, but it would be cool if there were more realistic features on it. I would like to see roads that follow realistic paths over the terrain, and not have them winding all over the place for no reason. I know that they have to be a certain length to make the trucks travel at a certain speed, but that's a whole other topic on how the convoys work. I also think the roads should not climb or decend very steep hills, nor should they have bridges randomly placed for no reason. Why would there be a bridge on a road on flat ground with no water?
The new trees are nice, but they need to be trimmed down in size and removed from runway ends.
Airfield placements seem kind of odd in some cases as well. Like when both ends of a runway face a hill for example.
I certainly don't like how small bodies of water seem to form a pattern when viewed from a couple thousand feet up, nor how some of those bodies of water are magically held in place on the side of a steeply sloped hill.
Snow would be nice at higher elevations.
Finally, sort of a terrain issue is the clouds. They look cool from far away, however they seem to have no effect on vision, as you can see right though them. The upper layer is too flat and you get no feeling of flying through it. You are either under it or over it.