One of the things that I find really irritating and cannot be solved through the 'Reduce Transparency' Accessibility option is the way in which the desktop looks horrendous when under the translucency of one of Yosemite's overlays. For instance, in the login screen and when you go into Mission Control, Yosemite makes the desktop behind it look like a horrible mess of gradients. This is true on a Retina screen, and it's even worse on a 1080p screen. While not 'elegant', the dark grey in Mavericks looked wonderful by comparison. I wish there was a way to alter this in Yosemite.