Luke Wroblewski has written another insightful article on designing for iOS 7:
The design language of iOS7 is inherently simpler than the one Apple used in iOS6. On the surface, that would seem to make designing for it simpler as well. But in reality you end up needing to do more with less, which is not easy.
In our iOS6 design, we had relied on depth (shadows) and texture to separate items in the list from each other. When we adapted to an iOS7 design, simplify flattening these elements once again created hierarchy issues. A number of of visual elements blended together too much making it hard to distinguish individual polls in the list.
It was only after we started to remove visual elements from the poll list that the flatter, simpler look began to work well. We took out the elements that had been background textures, eliminated icons, and introduced a bit of color to separate out actions like Comment and Share.
Removing texture and depth forced the rest of the visual design to work harder to create meaningful distinctions between the various elements on screen. I think this is a key reason why designing for iOS7 is harder. It forces you to simplify in order to provide the same clear visual communication using less visual relationships.