The Mark II is now boasts a faster and more importantly, more accurate autofocus compared to the Mark I. The AF snaps almost instantaneously and there were no back-focus issues that I felt plagued my Mark I. Photojournalists, wedding photographers, and event photographers, will benefit tremendously from the near-instant and accurate AF speed.
Quoting from the conclusion:
The new 24-70mm Mark II is such big improvement over the Mark I that I now shoot over 25% of my portrait and engagement session images with this lens. I have come to prefer it to the Canon 16-35mm f/2.8L whenever I do not need the extra wide angle. There are even times, and it is crazy that I am saying this, I preferred it to the Canon 50mm f/1.2L because the bokeh was good enough and gave me the extra flexibility in zoom.
The Canon 24-70mm f/2.8L Mark II gets a rating of 5 out of 5.