This is really a value for money. If you're budget is limited and looking for a decent all around/portrait lens, then look no further. My copy is very sharp wide open, nice contrast/saturation, and may not have the best bokeh around but has very decent quality.
If you need wider lens, then his brother 17-50 2.8 is another state of the art lens to check out and own.
However, if budget is not an issue, I'll think twice in getting 3rd party lenses.
On the other hand, being practical and the fact that I'm just a pure hobbyist... Tamron 28-75 2.8 or 17-50 2.8 is really one of the best thing that happened to camera world. I'm very happy to own and use one.