If we look at this just as a lens for a camera system then the cost is about right and the performance is excellent. So, for users of this system this is a very fine standard zoom and in fact pretty much the only choice at the moment. It absolutely delivers the goods.
Excellent sharpness, Low central CA, Performance well maintained at all focal lengths, Smooth bokeh, High quality manufacture, Weather sealed, Excellent ergonomics, Silent and ultra smooth AF, Image Stabilisation
Edge CA, Distortion