Shooting portraits at f2.8 is a pleasure, with nice bokeh -- the smooth blurring of out-of-focus backgrounds to keep them from being distracting.
The autofocus is reasonable, though louder and not as fast as on rival Canon telephotos I've used in this zoom range. On a few rare occasions, the lens autofocus objected with a bit of vibration when having trouble locking onto the subject. The lens makes no pretense at being a macro, with a close-focus distance of 1.4 meters; the Canon competitors' close-focus distance of 1.2 meters a significant improvement.
The included petal-shaped lens hood keeps lens flare under control most of the time. The lens also comes with a tripod mount.
The lens is heavyish but par for the course given the full-frame support, durability, and wide aperture. It weighs 3.15 pounds (1.43 kg) and is 3.4 inches in diameter by 7.8 inches long (8.6x19.8cm) without the lens hood attached. It's easy to shoot with it handheld, though not nearly as easy as with the smaller, lighter Canon EF 70-200mm f4L IS, especially after a full day carrying it around.
Sigma has been bringing anti-shake technology to its lenses, designated by OS (optical stabilization) in the name, and I found it very useful on the 70-200mm lens. A side-mounted switch can disable OS, configure it for ordinary use, or set it for horizontal panning situations like trying to photograph a moving racecar. I could capture shots with exposure times as long as 1/10 sec. when zoomed all the way to 200mm -- though certainly not every shot. The OS is quieter than on many Canon lenses, too, which is welcome when shooting video.
The lens is available with Canon, Nikon, Pentax, Sony, and Sigma mounts.
This Sigma 70-200mm doesn't match Canon's telephoto zooms for top-shelf sharpness, but it's a very good lens.