When Tim Cook said that iOS 7 was the biggest change to iOS since the introduction of the iPhone, he wasn’t kidding. The UI is of course drastically different, but things like background-updating and better car integration are huge changes.
However, once we can all zoom out a little bit, I think iOS 7 will be seen as an evolutionary change. A big one, perhaps, but one that shouldn’t be seen as all that surprising.
iOS 7 is a new foundation. This is how Apple rolls.