The Canon EF16-35mm F2.8 USM ii lens is chunky; distorts considerably at the widest angles and apertures and vignettes like it has an instagram filter inside it but takes some of the most amazing landscape pictures I have achieved. On my camera the zoom ring and manual focus rings are both smooth; and allow for clean focus pulling if you are shooting video. Even on my Canon 6d the (full time overridable) autofocus is pretty quick from shortest to infinity focus and the autofocus results in sharp images. The body is plastic with a metal body mount; if you add a (UV) filter - its an 82mm thread - the lens offers weather sealing (the zoom does move the lens in and out of the body of the lens so there is also a high likelihood of ingesting dust in its use so the filter should help reduce that too. Finally in the box you also get a lens hood; I found even without it I was able to take images in pretty much all circumstances without getting any flaring but its there if you need it (and the lens hood for the 24-105 fits inside it if you want to save some space)
I have dragged it around Bangkok and Singapore going in and out of air conditioning and tropical rain and the weather proofing kept it going; its super wide angle lets you take some amazing shots of the city Day and Night hand held getting everything in the frame without having to resort to stitching. With the aperture closed all the way down to F22 you get amazing sparkles on all the lights ( i have uploaded a full frame and cropped image showing the effect) ; and at F2.8 you can get images in lower light that you wouldn't be able to achieve with the 17-40mm F4 without extending the ISO / Shutter speed to difficult levels.
If you have a cropped sensor camera you should look at the Canon EF-S 10-22mm f/3.5-4.5 USM Lens
although note it has a higher min aperture and its variable which isn't so good if you want to shoot video, its considerably cheaper - on a cropped body the 10-22 takes great shots over the same wide angles as the 16-35mm offers on the full frame. Despite the distorting issues that you should expect with a zoom-wide angle lens with a tool like Adobe Lightroom
you can easily remove or reduce the distortion of the lens and are left with simply fantastic sharp images day and night.