Without a doubt, this is the best DX mid-range zoom out there. It's expensive, yes. But you get what you pay for: brilliantly sharp optics, even wide open; fantastic bokeh; beautiful colours. Prior to purchasing this, I'd tried out both the Sigma 17-70mm and a few copies of the Tamron 17-50mm. The Sigma comes nowhere near close. The Tamron is fine. However, it doesn't have the sharpness of the Nikon. Nor does it have the wonderful bokeh nor the colour rendition.
The build quality of the Nikon is of professional quality. This thing will last you for years. Yes, it's heavy and built like a tank and is not for the faint hearted after a long trek. And it costs up to three times more than the Tamron (although you can pick up a good copy for around £550 if you look hard enough). But, put this thing onto your Nikon body and it will take it to another level. That is something the Tamron won't do.