Will give you the extra stops in low light.
color, contrast, clarity (sounds like a diamond) are incredible.
You can shoot at f2.8 all day if you want with incredible results and no degrading.
Heavy. Large and sometimes intimidating to be in front of.
I don't like the location of the AF/MF switch and IS switch I seem to turn them off with my fingers without noticing I do it. Could have a better location for those.
I think for 35mm portrait work, fashion, and glamour the quality of the images and the lens are the best. But I have to admit that after shooting for four hours my arms, shoulder and back are stiff.