I see myself as mostly a portrait photographer and I have a lot of good lenses that cover the 50mm to 200mm focal length range. I have a lot of good choices when it comes to do a nice, tight portrait but I fumble a bit at the wide end. I have the Nikon 25-50mm f4.0 and it's fun and can be really good but using it for finicky commercial stuff is slow and I always feel that I should be in live view to make sure the focus is on the money. I've also got the 24-85mm f3.5 to 4.5 Nikon Zoom and while it's a very, very good step up from a kit lens it's not "ultimate" in image quality at any one focal length. Nor is it particularly fast (as in wide aperture).
I've recently toyed with the idea of getting the new crop of Nikon f1.8 wide angles; the 35mm, 28mm and 24mm but the thought of paying for all three (nearly $2,000) and carrying all three around and changing between them in a dusty environment gives me pause. Then this comes along and it replaces all three of the Nikon options in one swoop.
The Sigma 24-35mm is an f2.0 optic. Amazing. Wonderful; especially if it's sharp and geometrically well-behaved. This is one of Sigma's Art series lenses and the vast majority of user reviews and reviewer reviews say that pretty much every lens in the Art line is superb. Sigma states that, in the focal lengths covered, this lens is the equal to their own individual, prime lenses when it comes to imaging performance.
The lens is also usable with their USB dock which will help micro adjust any focusing discrepancies for users.
I haven't seen a price on it yet but if it's under $1,500 I'll take it. If it's around $899, like the rest of the lenses in the line up I'll take it and be thrilled. I'll wait to see how the smart people review it before I actually spend the money but I'm impressed with Sigma for the recent spate of fun innovation.