I used the original 24-70 f/2.8 for almost 10 years before upgrading it to 24-70 Mark II this week (to accompany my new 1Dx). I am not a lens technician, but as an avid photographer, I can attest that this lens looks substantially better than its predecessor. It is lighter, better designed, and produces really sharp pictures. I am enclosing a low-resolution casual hand-held shot for your reference (taken at night in available light - f/2.8 @ ISO 3200). Well done Canon!
I am waiting for the weekend to cover an event, and report back to you later.