I absolutely adore your iso houses, but there are two things that don't quite look convincing to me, namely the water and trees.
The thing about water is that if you view it from certain angles, it reflects. If you want to get technical about it, you can look up Snell's law and total internal reflection. I think for water, the critical angle is around 48 degrees or so. In other words, if you look at it from an angle less than 48 degrees, it will reflect. Anyway, I'm not sure if this is the case here, but I think it would make it look more natural.
Trees look complicated, but their design also follow certain rules. Leaves tend to be spread out in layers. This is so that the tree can get the most surface area for absorbing sunlight, and each branch has a cluster of leaves. Each cluster/layer casts shadows on the one below it, which leads to the effect you see with the brightest green where the layer ends next to the darkest green where the shadow is. Of course, this doesn't apply to fir trees in the same way since they don't have large, flat leaves. (Edit: On further inspection, it seems to be more related to density of foliage than size and shape of leaves/needles. Some trees have rounder clusters, and some have more like upside-down v-shaped ones.
Anyway, look at some trees to see how to mix shadows and highlights for different types of trees.
) There's also a ratio between the size of the trunk and the size of the crown. I don't think I got the shape of the edited tree quite right, but if you look at some pictures or find some trees outside, you'll get a better idea of how to draw them.
Hope this helps!
