I did an enormous amount of research before buying this lens comparing it to Canons 10-22mm and the other manufacturers equivalents. Although most reviews were positive in terms of performance and price there was some adverse comment about Sigma variable quality control.
In the end I bought this lens. It looks and feels quality and at first glance the images are as you would expect. However, on closer examination the images were not sharp at any f-stop or focal length I tried and the colours/contrast were awful. In the end I did a comparison with my Canon 18-55mm kit lens using two different bodies. With both lenses set at 18mm using the same shutter speed and aperture the "cheap" Canon lens was so much better in every respect that the Sigma 10-20 went back to the supplier the same day.
I have another Sigma lens with which I please but maybe the comments about their quality control are justified and I was just unlucky?