There's two things I don't like about the Nikon D600's images:
1) Some details, especially facial tones, can look smeary and fake. Almost like there is far too much make up.
2) When used with a flash, forefront objects that are primarily lit by the flash can render the object or person in a very two dimensional manner. Like a cardboard cut out.
Both these things can be seen from the below wedding photo I shot recently. The bride is rendered very unnaturally. You will notice that the brother of the bride is rendered quite well.
This image was shot with the D600, Nikon 24-85mm f2.8-4 and a Nikon SB800 flash. It was used on aperture priority at f6.3 at approx 50mm, colours set to vivid and flash set to +1/3 of a stop over on bounce flash with 9ft ceilings.
Anyone have any ideas as to why this might be the case? Is it the mix of flash and tungsten lighting? The veil? I am not sure.