me again,

I've this character I've moved over form ZBrush using GoZ. I've created UV's, textures and normal maps all within zbrush.
A very quick test render shows everything is reasonably OK, with the exception of the face; where I'm getting this weird shading.
I've tried a few options - tangent, adaptive, set to face, unlock etc. but it's still off.
I know nothing about normal maps, but the generated map seems very 'colourful' compared to the other maps created for the rest of the geometry.
there's one standard directional light pointed straight at the model, as seen in the screenshot.

any advice on where to start?