Combine Marco and Gruber's [1] insight - This is a major house cleaning/forest fire. Someone (Jony, et al.) has stepped back, looked at the confusion that has developed over the last 3-5 years on the iPhone, and has decided to recreate the iPhone as a conceptual platform. The introduction (and hopefully consistency) of multiple dimensions onto the phone, and a cross-system approach towards geometry, means that iOS7 will be a complete re-think of how applications work and behave on the iPhone.
And don't be so quick to say, "or even what Android and Windows phone offers.." - Those are awesome platforms, and Apple can learn a lot from them (as Android and Windows have learned from the iPhone.) Indeed, the "Cards" approach in multi-tasking is actually reminiscent of what Palm's WebOS did [2] - so Apple has learned from them as well.
I am very intrigued as to how well the Multitasking/Notification driven background/User-interaction-Dependent-CPU-scheduling-for-background-processess will work - That's pretty innovative solution to a common problem of Craptastic background apps that you don't think about sucking your battery dry. [edit: And all the discussions about Apps checking in when you've got the radios on, when you are powered up, etc... - I've been dreaming about exactly that for 2+ years. Finally! (Non-ironically)]
Don't kid yourself - iOS 7 is the big one, and, will likely be as ugly as the upgrade was from 10.6.8 to 10.7.0 was on OS X - My prediction is that iOS 8 will basically be fixing all the glitches and problems created from this complete platform rethink - but, sometimes, to make an omelet...
Forest Fire Indeed!
[1] http://daringfireball.net/2013/06/ios_7_signature
[2] http://www.youtube.com/watch?v=c20uhGxSxWo