Best general purpose lens I have owned. Incredibly sharp IMO - not sure why some people say it is a bad lens. Hythe, England at dusk.
I wonder if this is because there is more sample variation with this lens than others. Canon have turned out thousands of these at a 'reasonable' price and I suspect they're not all assembled to the desired tolerances.
However being a Canon L at least it can be 'post manufacture' fine tuned by specialists, unlike zoom lenses that have elements glued in.
At Building Panoramics we have two: one is perfect, the other is as sharp as a 50mm f1.4 (at say 5.6) on the far left, but quite blurred on the far right.