Agree with the almost-amateurish feel to those icons. Many of those icons seem ill-proportioned to me, especially the icons for Messages.
You've got a really different view of something ( a gradient ) outside of it context ( the whole UI ) and the same element as part of a whole design. That wasn't pretty obvious to the great super-pixel-detailed skeuromorphic design, where each icon was a whole design, but I'm pretty sure we'll speak differently by the end of the year when we get that iOS and evaluate the change for real.
Take a look at their new demo paga [1] it looks pretty nice and flattened. I'm afraid of what will happen to the 3rd party apps, that will not get a flat-design update.