this lens and some other high quality Sigma Zeiss lenses are the reasons why I just sold all my Nikon gear.
you may not be able to use some of the best Sigmas and Zeiss primes on Nikon any more, Nikon tries very very hard to just restrict use of third party lenses.
I think it will hurt Nikon since this will really narrow F mount ecosystem.
anyway, I briefly tried it at CP+ event in Yokohama this feb , it is big but not as big as my Zeiss 135mm f2 APO or 100mm f2.
it is about the same size as the Canon 135mm f2L , the Sigma is a bit shorter in length , though.
it felt about as heavy as my 100L macro lens or my Nikon 85mm f1.4G, I could not use my SD card in my 6D at the time , so I do not really know how sharp it really is, but it seemed very very sharp and well corrected.
I think if it is really this cheap , I would get 2 of these.
but what I really want to see from Sigma is a new Art line of 85mm f1.4 lens.
I like the 85mm L I had it but it was just too fat to hold and kind of awkward in real life use.
I also had Zeiss 85mmf1.4ZF2 but it was not a sharp lens at f1.4, and I sold it.
I am also interested in a great AF 135mm f2 prime but I think it is extremely tough to beat the Zeiss 135mm f2 APO,which is the sharpest lens I have ever used(sharper than the Leica 125mm f2.5 S mount lens).