I tested this lens against the Nikkor 28-70 f2.8 pro lens (I take this as the gold standard) and it is optically indistiguishable for practical purposes, except wide open, when there is a little vignetting (this only applies to film - a DX sensor is small enough to avoid this). It is lighter in weight but still solidly built. Switching to manual focus by pulling the focusing ring back is a useful feature (saves fiddling with the switch on the camera body).
The only negative, compared to the Nikon, is the mechanical focus, which is slower than the Nikon's electronic focus. Occasionally I have had to re-mount the lens on the camera to get the focusing mechanism to engage. But at a third the price of the Nikon f2.8, this is a really good lens. Optically superb - you would need to go to prime lenses to get better performance.