I'm not sure how I missed these, but Canon China has posted same images from the upcoming Canon EF 16-35 f/4L IS. The images look good, and the corners look better than the EF 17-40 f/4L. However, we won't know for sure how much better the lens is until we get some real world reviews. View the sample images here.
Preorder the Canon EF 16-35 f/4L IS $1199: Amazon | B&H Photo | Adorama