How do you guys handle shading in a 3d game? I have a directional light source that shades one side of a tree made of cubes. The remaining 3 sides all get ambient shading only. So the 3d effect is lost when looking at two ambient shaded sides. Am I missing something? Should I be shading the side furthest from the light source even darker? I tried looking at Fallout 3 and it kinda looks like this is what they do however Minecraft appears to shade a grass mound with two opposite sides light and the remaining two opposite sides dark kinda giving the effect that there are two directional lights for the two light shaded sides and ambient light for the dark shaded sides.

How does one handle shading in a 3D game? 

I have a directional light source that shades one side of a tree made of cubes. The remaining 3 sides all get ambient shading only. So the 3D effect is lost when looking at two ambient shaded sides. 

Am I missing something? Should I be shading the side furthest from the light source even darker? I tried looking at Fallout 3 and it kind of looks like this is what they do, however Minecraft appears to shade a grass mound with two opposite sides light and the remaining two opposite sides dark, giving the effect that there are two directional lights for the two light shaded sides and ambient light for the dark shaded sides.