Great lens for the money. Lightweight, metal mount. Very fast and silent USM focus. The focal length range is excellent on a FF body and still very good (or just as good, depending on how wide you shoot) on a 1.3X crop body. On a 1.6X crop body, I probably would have used it on the street.
Naturally, like most lenses this benefits from some stopping down. At f/5.6 and f/8 things look pretty sweet. CA is minimal throughout the range and not critical, IMO. At the wide end there is noticeable barrel distortion and there is noticeable pincushion distortion at the telephoto end. They won't be critical in most photographs but my present as bowed lines in some landscape photos with an obvious horizon line, or architectural photos.
The copy I had exhibited zoom creep when the lens was pointed downwards but it's not a consistent phenomenon.
The front element does not rotate so it makes it easier to use a circular polarizer. Do note that the lens seems prone to flare as well so use the hood whenever possible. That said, the hood will not solve flare issues in all circumstances and you'll need to hold your hand out to shield it from the sun, quite an absurd proposition if you're shooting handheld.
Overall in practice, this was an excellent lens. This lens did over 95% of my photos in a recent New Zealand trip. For me, the range was simply magical on a 1D: