Here is a summary of S.T.A.L.K.E.R.'s DirectX 9 capabilities:
S.T.A.L.K.E.R. is capable of more than 2 million fully bump-mapped polygons per frame as well as true per-pixel complex light-material interaction.
By targeting the latest hardware we have been able to base the engine fully on HDR (High Dynamic Range) lighting to increase the quality by addressing unnatural over- or under-exposed visuals found in traditional renderers.
Natural render of complex materials with proper light interaction, such as rusted metal, natural flora, glass, skin, and so on. In addition, every pixel (not texel) can have its own material with several coefficients.
The custom-built dedicated renderer is capable of real-time dynamic lighting, soft (physically correct) shadows cast from every object onto every other object, true per-pixel lighting, physical umbra/penumbra computations, and hundreds of lights per frame--all in real-time.
Frame buffer postprocessing and Photoshop-like effects.