i got that same exact lens. i got more than a year na.. 
i find the lens sharp sharp.. be sure to put on a lens hood since may ma flare sya minsan... what body are you using with this lens?
for d80 and lower di siya nag f2.8..the widest is f3... but if you use a d200 or d300 kaya nya mag f2.8...
Yeah may compatibility issues siya, And yes it works both on Nikon and Canon. Im using it with my 2 EOS Film SLR bodies 500N and Kiss. Works pretty good and yes sharp nga siya hehe, those who are looking for a CHEAP wide lens with macro that can go with dim lights i recommend this lens. Here are some sample photos for reference:
Gears used :
Body : Canon EOS Kiss
Lens : Sigma Super Wide II
Film : YKL 100 and Kodak Colorplus 200
For the street shot, sa hotel room ko yun sa Changsha Hunan China, used a CD - R King tripod then shot with long exposure. Dun naman sa Cave shot aperture priority mode with no flash and tripod.
Thanks!
