I too was a late adopter of Yosemite. Just upgraded about a week ago.
It was a great decision. Yosemite enables so many new features/capabilities, not the least of which is KM7. KM7 is totally awesome, adding so many new great features.
BTW, my Yosemite upgrade went without any issues.
Finally, if you don't like some of the UI features, there are ways to deal with things like the transparency.