Superb build quality, very sharp, and I like the push-pull zoom.
Overall this is an excellent lens with only two issues, one issue is major to me, one is minor.
First the major: the BOKEH (background blur) has a very unusual look to it...I've noticed it on not only my pictures but anyone's pic with this lens and a large apeture. I'm not sure how do describe it, other than the bokeh looks almost fake, like it was produced in photoshop (Actually, I think photoshop does a better job!).
Then the minor: you WILL get noticed while using this lens. Nearly every time I use it someone has to comment on it.