Rounding corners and harmonizing colors is nice but it's not what I care about. I wish they'd demonstrate their awesome design skills by working out a reasonably intuitive UX to do nested sorting. And do so without losing any existing functionality.
Another example is Firefox. Almost every UX change in the past two years has made the browser noticeably worse and requires serious users to hack CSS under the hood to fix. They keep taking things away and rearranging deck chairs while not adding obviously missing functionality like a non-right-click menu UX to manage sidebar lists.