I deliberated between this and the new Canon 24-70 2.8 for quite some time. Reading, watching everything I could.
I put her through the first round of testing today - sharpness. I started shooting some fine print from across the room which wasn't a very good idea, then I defaulted to my all time favorite sharpness test. Shooting my African Grey Parrot, Jake. Take it from me, if a lens can resolve the individual vanes in a bird's feathers (at 2.8), it's sharp enough. My copy did. It's also VERY well built.
Tomorrow, just for grins, I'm going to pit it against my 24-105L and compare distortion, color, CA and contrast. I expect it to be more distortion free.
Best of all, so far, is it cost me under a grand, brand new with a 7 year warranty.