I used the Canon version of this lens, and was disappointed for what I used it for, indoor gym sports (volleyball). The issue/problem was that the zoom ring was STIFF. As I see it, this is due to a design decision. The zoom ring has a relatively short throw, from 17 to 50mm, significantly less than 90 degrees. This short throw, then requires a steep zoom cam, to trombone the lens out. this steep cam, then requires more force to be applied to turn the zoom ring. I would have preferred a longer throw zoom ring, to get an easier to turn zoom ring.
If you do not shoot sports, and are not constantly zooming the lens, as I do when shooting sports, the stiff zoom ring may not be an issue for you.
BTW, for you Nikon guys, the zoom ring on the Sigma lens that I used turns in the opposite direction than the Nikon lens. This is not an issue for casual users, but for anyone doing fast action, where muscle memory works the zoom ring, you could miss the shot when you turn the zoom the wrong way.