Sold the 24-70mm to get this one and it was a nice trade off.
My 17-55mm is sharper, bokeh and color is in the same quality (L glass), and itīs much much lighter and smaller.
Itīs nice to have a Canon L glass with f2,8 that coverīs the normal range, has IS, USM, and only have to pay $1000.
There is no EF lens that beats that! or even comes close to that on a crop body
Image quality I get from this lens is amazing. I have used canon 70-200mm f2.8L, canon 28-70mm f2,8L and canon 24-70mm f2,8L and 17-55mm is my favorite regarding image quality.
I think build quality is very nice except that it has plastic filter mount. If it had L build quality it would have been much much more expensive probably around $1400 and 200gr heavier.