There are still many rough edges in the new OS but overall I am really excited about the visual direction that Mac OS X Yosemite is taking. It demonstrates a more mature and subtle approach in adapting iOS 7 design language. No ultra thin fonts, no crazy parallax, no ridiculous icons, just subtle use of translucent materials accompanied by a bright and cheerful palette. Using the new OS feels fresher, exciting, and more modern. I am looking forward to exploring other design changes in the the new OS that I may have missed.
Something else I've noticed: is it just me, or does Apple use a different theme on-stage during a keynote than what actually ships in the beta right now? The transparency and colours pop way more during the keynote than while using the beta. Odd.