8 out of 10 points and not recommendedBuilt like a tank, fast focusOptics could be better, bokeh
Let's start with pros - I really like the build quality of this lens, which is unusual for Sigma. It's built like a tank, metal barrel, zoom and focus rings operate very smooth, nothing to fault here. Also the autofocus is really silent and accurate, another plus for Sigma.reviewed June 8th, 2010
Now what I didn't like: sharpness is ok. Not great, but usable. CA's (it's not true APO lens after all) as well. Completely useless as a portrait lens - while f4 is fine at 300mm, having the same at 100mm means that the DOF control is rather poor, also bokeh is simply horrible.
All in all it's not a bad lens, however it can't compete with 70-200 f2.8, especially stabilised ones.