I wanted a fast 50mm that would provide good sharpness wide open with with a quiet, reliable focus. After reading tons of user and pro reviews, I decided to give this lens a shot. My only concern in purchasing this lens was the reported potential of front/back focus issues.
At the time I was ready to purchase, Sigma was providing a $100 instant rebate and I decided to pull the trigger on the purchase. It has turned into one of the best photographic purchases I've ever made. Upon receiving the lens, I put it through extensive focus tests and ended up with a -2 setting on my focus adjust. It has also proved to be very consistent.
Sharpness wide open is very good and razor sharp from F2.8. Focus has been very consistent, quiet and quick enough for most any situation. My copy has the more recent smooth finish that gives it a polished, professional look. Build quality is excellent and the widely reported large size and weight gives me good balance with my camera and grip. Vignetting and corner sharpness are non-issues on my APS-C camera. Bokeh has so far been smooth and very pleasing.
Most importantly .... it consistently provides images that are noticeably better than I would of ever expected.