I can see some appeal for this lens, e.g. astrophotography.
To me this lens is interesting because it breaks the f/2.8 zoom lens barrier. Sigma, how about a 50-135/1.8
and how about a 16/1.4 while you're at it? Please....
What did you expect ? I thought it was more.
I guess that's what felix intended to express: the low price made him reconsider his plans to switch to FX...
-- Markus
Editor
opticallimits.com
Markus is correct. I did not expect this lens to be significantly cheaper than the Tamron 24-70 (or even the Nikon/Canon MkI), due to the rather extreme design and unique market position.
I think Sigma has made this lens quite attractive now. You can get a D7100 & the 18-35mm for only ~300€ more than a D600 without lens.