This was a very good wide angle zoom when first introduced. It’s still considered very good, although certainly not the caliber of the Nikon 14-24 f/2.8 lens.

If you’re doing landscape work and shooting at f/4 or higher, the Canon 17-40 will provide every bit as good of an image at a lower cost. If you’re shooting on a crop sensor camera (T3i, 7D), the 17-55 f/2.8 IS EF-S offers nearly as good an image quality, plus the added benefit of image stabilization. If you need to go as wide as you can get, the Canon 14 f/2.8 is wider with better image quality and less distortion. And if you don’t mind a bit more distortion at the wide end and are not concerned about sunlight flaring in the image, the Tokina 16-28mm f/2.8 is at least as sharp as the Canon at a better price.

All of this isn’t meant to sound negative. The Canon 16-35 travels with me everywhere because I need the convenience of a zoom, and sometimes I need f/2.8 on my full-frame. In my mind, the 16-35 II is to the wide end what the 100-400 IS is to the long end: a very good do-it-all lens. There are specific lenses better for specific tasks, but the 16-35 is good at everything.
March, 2013