The design of iOS 7 is based on rules. There’s an intricate system at work, a Z-axis of layers organized in a logical way. There is a profound reduction in the use of faux-3D visual effects and textures, but iOS 7 is anything but flat. It is three dimensional not just visually but logically. It uses translucency not to show off, but to provide you with a sense of place. When you pull the new Control Center panel up from the bottom of the screen, its translucency lets you know that you haven’t gone somewhere new, you’re just looking at something over where you were.
If you read all that and you’re still interested, you should click through for the rest. I’m interested to see how iOS 7 turns out in practice, not just in screenshots, but Apple seems to be moving in the right direction.