The 3D Depth controls the amount of "pop" you will get with 3D images by shifting the "left" and "right" images further apart or closer to together. On the other hand, 3D Viewpoint is only available while using the 2D to 3D conversion feature. It will give more "depth" to the picture by adjusting adjusting the spacing of the background in relation to the foreground.
If you have any more questions, please let me know!
LG WRman Sherlock, out!
EDIT: I had some mistakes in my information, and I corrected it.