Good lens overall, at least for this price it won`t get much better. Sharpness, AF speed, noise level and color rendition are all good but not stunning. The DF function is a pain because it`s just something more to fiddle with (why do they build that mechanism when it does not work in such an obvious way???). Generally, DF is a good idea, but, well, read above.... Pincussion distortion @ 70mm is another problem. If you`re shooting @ said focal length, make sure there are no straight lines near the frame borders or they`ll turn out heavily bent. Not so good.
Apart from that, everything`s fine. The lens feels good, everything is in the right place, just under the appropriate finger. It is fairly fast, not too loud, aperture ring is VERY comfortable and picture quality is solid (which is most important, innit?). Bit warm, bit soft sometimes, not bad really (i tend to really like the warmish color rendition). If you`re on a budget, buy this lens immediately, if you`re not, well, you might want to invest in both a sigma 28-70/2.8 EX DF AND a 100-300/2.8 IF HSM rather than going for only one 28-70 AF-S or L lens....