Okay, I did some tests for non-metallic surfaces, used UnrealEngine 4 with some stock PBR textures to have a valid reference:
And in Doom3PBR:
The result is very impressive, shading model looks correct. I suspect the biggest problem is idtech4 lights that may be incompatible here. This light cone/hotspot behaves strangely when you move, and when you get close to surfaces, they become too shiny:
But when that gets fixed, it will look as incredible as in UE4.
In the meantime I'll test some metallic surfaces too.