NOTE: there is a shiny silver "A" on the side of the lens in the picture, meaning this is their "Art" line of lenses - the same breed as the 35/1.4 that has blown away many many people.
Yea, there's a silver A on the side, but this lens doesn't really fit into Sigma's own definition of what an 'Art' lens is going to be. At least not at the time they announced this:
Art – These lenses are developed with an emphasis on artistic touch and are designed to meet the expectations of users who value a creative, dramatic outcome. Along with landscapes, portraits, still-life, close-up and casual snaps, these lenses are perfect for the kind of photography that unleashes the inner artist. Ideal for studio photography, they offer just as much of an expressive scope when capturing architecture, starry skies, underwater shots and many other scenes. This category will be comprised of many focal lengths and designs, such as large-aperture prime lenses, wide-angle lenses, ultra wide-angle lenses, and macro and fisheye lenses.
"This category will be comprised of many focal lengths and designs", might also include Super Sharp Constant Aperture 4.375 Zoom lenses with little or no distortion.
I was hoping Canon might come up with an improved 24-105 II, but this Sigma just might fill the bill.