Pros The range is excellent, and despite the non-USM focusing, its quite fast in terms of focusing and not loud. Would be nice if it were a little faster aperture-wise, but the IS works very well. For anyone but a pro, a terrific lens.
Cons A little bit soft at the edges. Pros and pixel peepers will gab on and on about IQ not being the same as an "L" lens, but for the rest of us, very nice. Barrel distortion only noticeable on buildings or fences - easily corrected.
Summary For most users, this will replace all the lenses you normally drag about, whether on vacation, around town or for portraits. Certainly you will not get the same quality images as, say, an "L" lens, but in my experience, better IQ than any similar Tamron or Sigma, and I've had both. There's a bit of barrell distortion, but a quick hit in PLlens or DxO will fix that. The non-USM focus works faster and quieter than expected. For those worried that non-USM breaks the deal for them, you don't know what you're missing. I don't want to hear the pros chime in to bash this lens - its not aimed for you. Even so, great pro photographers, such as David Ziser, say they like the lens just fine. For the rest of us amateurs, you will not be disappointed. Give it a try - I'm very happy with it.