I have the older non-os (IS) 150mm macro and I LOVE that lens!!!!!! It is by far the sharpest lens I've ever owned.... and I've owned just about everything out there. I've never had L-series glass sharper than this. It's big and heavy for its size (thank goodness for the included tripod collar) and I see why they added OS to it, as handholding macro shots are nigh on impossible for doing shallow DOF. This lens is absolutely sharp at max aperture (f/2.8). I use it for portraits, macros, and detail shots where I want the best bokeh.