Love the redone traffic lights! For partially colorblind people like me, it's a great boon: the yellow and green are easier to tell apart.
Not that that's a big deal -- I could always tell by position and hover -- but still, very nice and slick-looking. I also like the menu bar much better, since it doesn't appear to be faded into the background anymore. Wish they'd make reflections in the dock less pronounced, however. At least a little more blurred. I've been using WWDC build and they're often distracting.