Normally we may think that we are designing 3D models, but actually I think we are not. Even though we're building a three-dimensional polygonal object, the final output is always 2D.
There is ultimately not much difference between painting and 3D modeling, because at the heart of it you're designing a picture, or sequence of pictures.
The only difference is whether it's created with two-dimensional methods or three-dimensional ones. So how realistically do you feel you are designing that 2D output when modeling in 3D?
Shadows are the biggest factor here. We are designing more for shadows than we are for the shape. The right shadow falls on the right place if the model is right, within a proper lighting scheme.
If the resulting composition does not seem strong enough, and if the character does not appear strong enough, it's very possible that the shadow shape is wrong. You have an incredible amount of control at the modeling stage, and it's here that you can generate shadow shapes quite flexibly (see Figures 6a and 6b).
If you can't hit the right shadow after hundreds of iterations, maybe the target impression that you are trying to accomplish differs fundamentally from your lighting.
Figure 6a: At the modeling stage you have the most control over shadow shape.
As a good example of this, film director Kon Ichikawa often utilizes light coming from the side, so the faces get a clear shadow cast from their nose even with less rugged faces of Asians. Half of the face would be in shadow if he tried this trick with Caucasian actors (see Figure 7).
Figure 7: Director Kon Ichikawa often lit his actors with strong cross lighting.
It would help to check the costume design of your character to see how a busy shadow runs across it, and you might also want to compare it with the complexity of the background. This will help you to establish and control the balance of shadow.