I'm not close to the 10 million population gap but it feels a bit rough...
In my opinion the regions bring a new landscape, a new whole city that you can create with specific stylish buildings, and it's enough for me... I enjoy the different size and borders of the regions ...
What I do think is a miss is that you never need what other regions produce : I mean in my case I don't have the canyon, and I never need to find canyon's objects for anything. The business is not impacted and is not reinforced and it's disappointing.
The new region storage is sweet but should me expanded a little, with region items, and not AGAIN storage specific items...
EDIT : It would be great to add a way to war map in regions.