why are opinions on the 16-35mm so varied?

I'm looking to finally take the plunge and upgrade from my d7000 to the d600. With that, I'll have to look for a new wide angle lens for FX.

From the posts i've read on the 16-35mm f/4, it seems people either love it or hate it. Some people claim the lens is too soft, while others claim its one of the sharpest lenses nikon has ever made. With that, I don't know who to believe. About the only thing people do happen to agree with is the massive distortion at 16mm.

Is the sample variation on different copies really that bad? I'm not really interested in the 14-24mm because I'd love to be able to use filters. Thanks!