Originally posted by djrocks66 You guy's that complain of the bouquet... What? This lens looks great! Sigma is doing some good things these days.
It's "bokeh" (or ボケ "boke" in Japanese). Don't judge bokeh by extreme closeups such that the background is completely obliterated, and you can't tell what you're looking at anymore. Any lens can do this, and this tells you nothing about the true character of the bokeh.
The problem that a lot of people have with it on this lens is how it renders high contrast lines in the background as a jumbled mess, and highlights as hard-edged circles, when focused at medium distances. Take a look at the top left corner (area around the statue of the guy on a horse) and in the fountain of this sample at 100% in DPReview's review to see what I mean:
http://www.dpreview.com/lensreviews/sigma-35mm-f1-4-dg-hsm/samples/bokeh/IMG_0095.jpg
Most people would not consider bokeh like this to be pleasant, though it doesn't look quite so terrible when viewing the image as a whole (i.e. not at 100%) IMO.
What makes this lens interesting to me is the extreme sharpness combined with subtle (not extreme) shallow depth of field at medium distances which really makes the subject pop out of the background, something a lot of people refer to as the "3D effect" (though it's more effective on FF with the wide angle).