If you don't like Yosemite, you should complain, and complain, and complain yet again to Apple.
Why do I say this? Graham Perrin posted a link to a video of an interview with Jony Ive (who I think is responsible for this mess) and in it he essentially stated that he really didn't know much about computers.
This is exactly what we DON'T need. From what I've been able to assemble, he's unaware of what are considered historical design "norms" like using 3D effects to segregate controls from input fields, the massive use of translucency and the hit it takes on hardware and performance seems to have been overlooked, the appearance of the UI on large displays seems grossly overlooked (as in, not tested,) and the effects translucency and the new, finer fonts have on people with vision that's less than 20/20. That's a few, but read the entire thread for more.
In any case, I'm under the impression that what Apple did was decide that since Ive did a great job with the cases for Mac's (one or more of them are in a museums of art) I guess they decided that since he was good at that, he'll do wonders with the OS. This is sort of like having a famed plastic surgeon, a specialist in the superficial and fads, being named head of cardiac surgery at a hospital, who then gets those that don't agree with him either forced out of the company or fired. Hey, that heart operation you just had may leave you with a heart that doesn't quite work right, but in the opinion of the overlord and grand master, it looks great.
Picture this:
Jonathan Ive decides that the way GUIs work are all screwed up. Instead of controls, force users to buy a trackpad, do away with all window controls all together, and force users to learn series of "gestures" to use instead. For example, you could minimize an application with a "pinch" operation. You cold bring back with some archaic tap three times with 2 fingers, or some such nonsense. Do you think this is ridiculous? I don't. I could easily see this guy completely destroying a perfectly good operating system and trashing it for his own (in his opinion) brilliant visions.
I'd also like to add that before the fan boyz or representatives on this site from Apple's marketing group offer yet another rebuttal using iPhone sales as an example, keep in mind that the iPhones are likely sold based heavily on the price of contracts plus the fact that they've finally made the phone a little bit bigger, which I'm sure appeals to many, especially those that found the original versions too small to see.
CHEERS!!!
I have the impression that Ive isn't particularly great at UI design and there is no one at Apple who stops him from rolling out his results.