I think what has happened is that Canon's pricing policies have become SO absurd that is has given some astute tech. and money managers at Sigma the ability to realize that they have a lot more wiggle room to make a great product and still be super competitive in price to big read. (it also shows how ridiculous Canon's pricing has become). I do not own a crop body either, but I do LOVE the appearance of this lens! Hope the IQ and price/performance ratio are right up there with the Sigma 35mm, f/1.4 that I own and absolutely love. This can be nothing but good for all of us! Can't wait to see what the next lens is in the new Art Line!!!!!!!
I'm actually tremendously interested in a new version of their 24-70/2.8 and who knows, maybe something like a 24-90/4. The Tamron is quite good, but Sigma looks like they don't want to be a "second choice" anymore. I love when 3rd-party manufacturers deliver such quality; they set you free from this or that system.
This is great for crop shooters. However, before everyone gets excited over the f/1.8 bit, you have to remember that f/1.8 on a crop sensor is nothing like f/1.8 on a FF sensor. This lens will give the same angle of view, image noise for given exposure parameters (*1), depth of field at a given AOV and subject distance (*2), etc. etc. etc. as a 28-50mm f/2.8 full frame lens.
In other words, if the lenses and sensors are perfect, this lens on a crop sensor would give identical results to a 28-50mm f/2.8 on a FF sensor. However, lens and sensor imperfections actually favor the larger format sensor, so don't expect this lens to give anything as good as the 24-70 f/2.8 original or the tamron.
Still, its great improvement for crop shooters (if it keeps up with recent Sigma trends), and should be relatively compact.
(*1) This considers photon shot noise only and assumes photos are rescaled to same resolution when printed.
(*2) At non-macro distances
Depending on the price point, the difference between a FF + 24-70 and DX + 18-35 might be what is truly impressive. This lens is not going to reach anything tremendous from an absolute perspective, but it's going to narrow the gap between crop and FF. Actually, I think it would make for an amazing travel lens since it would eliminate the need of a fast prime. If you want to travel light and bring only a crop body and one lens, you either go for a usual standard zoom and live with the slow aperture or you go with something like this.