The ultimate game changer?
I have owned this lens for some nine months. And while I'm not a professional shooter in any way, this lens is top notch quality from one end to the other. I was a bit skeptical at first, evidently being blissfully ignorant with my trusty old Canon 17-55 f/2.8 IS USM. However, I quickly came to realize that the Sigma outperforms the Canon in every possible way. A pleasant wake-up call from my then current Canon slumber.
The optical and image quality is superb. When (and if) I do get bad results, it's more likely due to my inability than that of the lens. It's built like a tank and if feels rock solid in your hands. The lens is arguably heavy, albeit, coupled with my Canon 7D, it's a perfect match and the weight has never been an issue. The exterior lens design is very pleasing and it looks fabulous! Of course, the low price and the constant 1.8 aperture is simply earth-shattering and without comparison. Sigma has rightfully challenged the Canon and Nikon hegemony with their new global vision lenses, and thus raised the bar drastically.
So far I only have to minor issues with this lens: 1) the zoom and focus rings are too well dampened for my taste; and 2) the ridges on the rubber rings are too narrow, resulting in a less comfortable grip and tactile sensation, while at the same time making it harder to clean off dust and specks without having to resolve to finer instruments (toothpicks, anyone?).
Other than that, it's simply a fantastic lens and quite possibly, hopefully, a game changer in the lens industry. Provided, of course, that the competition up the ante accordingly…