I can tell you one thing, the person who did the OS X icons did a hell of a better job.
Come on, it would be hard to do worse,
anything is better than iOS icons
I don't like the System Preferences icon though. There is something wrong with the way it scales down on non-Retina displays, the upper line in the cog looks weird sometimes (depending on the size), also the dimensions of the rectangle don't go well with other icons.
Also, I don't like the color of the Mail icon. It's too prominent. Or maybe the gradient should be more toned down.
There's something wrong with the way inactive vs active windows are displayed. Take Safari for example: when it's active, the window is darker (due to the transparency effect). Click the Desktop to make it inactive. It gets brighter, more prominent, which is a bit counter intuitive.
However, I must say I like the UI, on general. It needs some tweaking here and there, but it's better than iOS.