Sigma claims that this lens is a "pro level performer for shooting everything including portrait photography, landscape photography, studio photography and street photography", so I put it through its paces to see if that was true.

If you'd like the short version right here, the lens mostly holds up to those claims.

This review is more about how the lens performs in the field, and I haven't comparedit to any other lenses even though I have a couple of Nikkor 50mm lenses.
I didn't want the review to be about this-50mm vs. that-50mm. There are several other blogs and photography or tech-related sites that have made those comparisons. Skip to the Image quality section for links.