I'd add some high lights looks a bit flat.

you can use shaders. zbrush has some cool toon shaders I'm sure ya could make shaders in Poser.

matcaps are cool zBrush & Blender has them. Does Poser have matcaps ?

Topaz Labs have some cool 2D effects

App's like Gimp ,Photoshop etc etc have cool effects for them also.

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