This is the ideal lens for someone who shoots indoors using available or limited lighting. It is also excellent for landscapes and architecture, and with the extra f-stops, it gives lots of room for creativity. There is nothing else in its zoom range that is as sharp and has the bokeh of this lens. I shoot pics of small children playing and running around and this lens captures the moment better than anything else. I'd like use a 50mm f1.4 prime, but it is the equivalent of 80mm on a Canon EOS 20D, so I had to settle for the next best lens and this is the one. This lens will probably stay on my 20D most of the time. As far as Canon Luxus lenses go, the 16-35/f.28L is on par with the best.
The only down side is that this lens is costly. I tried to look for a used one, but had no luck and it seems that once people get one, they keep it. My advice is to save up and get one because it is definitely worth every penny.