I have used all kinds of zooms including the Nikon 80-200 2.8 and this is the sharpest zoom I have used..
Wide open it's very sharp and at 4.5 it is as sharp as a prime..
I still cannot believe that Sigma sells this 300 2.8 for the price they do..
I was debating between the Nikon 300 2.8 and this one,, but the ability to zoom out made me go with the Sigma...Sure some diehard prime shooters will doubt it's that sharp.... but as a long time shooter of prime lenses.. it definately convinced me....
Build quality is top notch,,,the finish is beautiful and a nice hood comes with it. .. the hood is a little short...
Oh,,and did I mention it's extremely SHARP!!!!!
Update... I've been using this lens for about 6 months now and it still amazes me..
I shot motocross races with it and the autofocus is extremely fast and accurate. I cannot even imagine giving this lens up for a prime 300.
The images are tack sharp...