I did find a couple of annoying things.
The visibility of the AF points is much poorer than on my 7D, where they are large and easy to see. They light up for about 2 seconds when focus is reached, while the 5D MK III just flickers for a instant. Its a very good low light camera, but it would be nice to see exactly where your focus point is in the darker scenes, and it washes out in bright sun.
It is slow to acquire focus in dark scenes, its very accurate, but can take a few seconds. My MK II did not do that.