I own the very first version of the case, the CM 690. I've been using it for 9 years now, and it has gone through many different components. Airflow is good, fits a wide range of components, etc. Cable management options could be better, but it's not terrible.
All that being said, looking at the new iii version it looks like they improved the cable management a lot. The cutouts have rubber grommits installed, the hole in the MB tray is nice and large. They removed a bunch of 5.5" bays and replaced with 2.5" bays which is nice. Better radiator compatibility, better dust filters.
Overall it looks like the changes they made fixed what I really didn't like about the first version. Of course I still use the first version so even those...