It just looks soft when viewing the images at 100%. Not an ugly soft, just a dreamy soft look. View it at normal screen sizes, and its fine. Use the Sigma 50/1.4 from about 1m + away from the subject, and its simply amazing.The only time it doesn't produce results where its bristling with detail is when shooting wide open near MFD.
What happens at MFD wide open? Reason I ask is that I frequently find myself shooting at that distance.
Maybe I'll play the Sigma lottery and order one from B&H.
As far as I know, many lenses are not at their best used near MFD. If you need to crop close, a good macro lens is the best way of increasing your chances of getting good results.
I decided before I ordered mine that if the second copy was no good, I'd get my money back and go for the Canon instead. With hindsight, I'd say its worth going to three or so to try to get a good copy. You really can land on your feet with the Sigma 50/1.4.