For the first few days I was dissapointed but later i have realised this is much better for shooting flats than the Zeiss 18 3.5 ZE i had before. It's great for wide angle shoots and ok for portraits at 35mm but I wish Canon would just make lens like Zeiss 15mm 2.8 for the price of the 16-35 4 IS
Versatile, IS is a killer good, distorsion in not bad; Sharpness is not too bad in corners
I guess it's sharper than other canon wide zooms but not as close as sharp as Zeiss 21mm 2.8 ZE; Out of focus part seem a bit weird as if they are result of camera shake