Summary: An essential piece of kit. I have never really liked zooms - even a cheap prime beats an L series zoom in my opinion, in terms of image quality. For example - try this lens against the 24-105 f4.0 L lens at 35mm - at f4 the images are quite obviously different in quality - the cheaper 35mm beats it soundly. The lack of contrast and fall off in the corners is easily fixed in DPP or ACR with lens correction selected.
Pros: 1) cheap, 2) reliable, 3) light and compact
Cons: 1) slowish and noisy focus, 2) not sharp at f2.0 - you need to shoot at f2.8 and up, 3) colors are slightly washed out and grey looking - not much contrast on this lens.