I rented it over the weekend and loved the portability. I never took it off center focus (with 5DmkII or 5Dc), but everything was plenty sharp, and the colors were great. It's true there is some considerable vignetting wide open, but not unattractive or unfixable. I did notice darker exposures than I'm used to, but just increased the compensation. I was really impressed that the lens produced no lens flare, even shooting into the sun basically. Here are some random samples (from my sister's wedding rehearsal) all at f2.8 with zero editing. I'll be buying this lens soon.