While this isn't terrible, I just don't get the big reasons for changes like this. We now have Retina capable Macs and we are moving back to "clip art" style icons?
I'm all for "deferring to content" and eliminating useless or over-the-top UI chrome (or wood shelves). But I like the photo-realistic icons and controls that Mac OS X had over the years. And shading and buttons/controls help people quickly find what they need.
And color! If there is one thing I'd want back in OS X, it is color. (yes, I have the hack to bring color back to finder sidebar)