The latest update to OSX incorporates design elements from iOS7. If you hate iOS7, you’re going to really hate Yosemite.
However, there are a couple of things you can do to restore screen legibility. Open up the Accessibility preference pane in System Preferences. Click on the checkbox labelled increase contrast. It automatically checks the box for Reduce Transparency. This does two things. First, it stops background colors from bleeding through menu bars and option panels. Second, it darkens the text so it is more legible.
That still isn’t enough for my non-retina displays, so I also move the Display Contrast up to the first tick mark. Finally, on the physical monitor controls I reduced the brightness a bit. I’ve been using it all morning and the text is readable. Unfortunately, there is no way to fix the contrast on buttons so that they are more readily identifiable, but I suppose I’ll get used to it.
Safari:
I like to see the entire URL when maintaining my websites, so in the Advanced Safari preferences I check, “Show full website address”. In the security section I turned off “Autofill web forms using: Credit cards”. Then under the View menu item, I turned on “Show Tab Bar” and “Show Status Bar”.
Dock:
In the Dock preference pane, I disable “Double-click a window’s title bar to minimize”. Prevents you from accidentally disappearing windows. This isn’t a new feature, but I just found out how to disable it.
My usual method for pinning the dock the bottom RHS corner doesn’t work, so if anyone figures out how to do it, pls let me know.
Finder:
In the General preference pane, change “Sidebar icon size” to large. Improves legibility.
Lots of other annoying things I’ll probably get used to, though it would be nice if someone figures out how to change the folder color in the Finder from the garish blue. The good news is that everything I’ve tried so far works just as before—including all the software I wrote.