About the only definitive statement that can be made about iOS7 is that it's polarizing.
I see this as a problem for Apple. Prior to iOS7, iOS was, across the board, more or less liked, even loved. There were some opinions that the design was getting a bit stale, but it was never really the source of large scale vehement hatred. That's largely due to the incremental design tweaks it saw over the years...the changes were not radical, but they were changes nonetheless.
In fact, iOS before 7 was the epitome of great design. Great design is design you barely notice. It stays out of your way. iOS7 requires considerable thought in many places. It requires squinting. It requires forgetting old habits from prior versions and relearning.
iOS7 feels completely off message. Some love the new message, some hate it, but it's an undeniably new animal, and as with anything radically new, there will be haters. Some haters will get used to the new beast, but some may very well may drop iOS and Apple altogether, since many people's entire relationship with Apple is based solely on iDevices.
Had Apple stayed the course and merely continued streamlining and tweaking things instead of rocking the boat so hard, they may not have lost as many followers. They definitely would not have lost iOS7 haters if the changes were not so radical. But they did rock, hard, and people will be vocal about why they left, and those vocalizations will spread. IOS7 haters that formerly recommended iDevices to friends and family and coworkers will rescind those recommendations, and stop making new ones.
And the very qualities that made iDevices so immensely popular....simplicity and intuitive ease of use, have been compromised. This means older people and small kids won't get it immediately. That means less impulse purchases in stores for newcomers.
Where iOS inspired near universal love before 7, iOS7 elicits "cool". It is cool in many ways. But it's a detached cool, bordering on cold and lifeless. For some, this is a minty fresh breath of air. For others, it's alienating and will mean a migration away from iOS.
