In fact, based on how people write their criticism, I have a very strong suspicion that the group which tends to dislike Yosemite the most are the self-proclaimed die-hard Apple users. Often the same people who complain how Apple tries to make OS X look and be like iOS and say that 'Apple is used to be so much better', 'Apple lost their way', 'OS X is being dumbed down', 'OS X is being locked down' and so on. The ever popular 'old good days' syndrome. Of course, by far not every negative post here is like that (there are some very insightful and constructive comments!) , but many of them go along the lines of 'I have been using Apple for 10/15/20 years, but Yosemite will make me move to Windows/Linux/RaspberryPi just because it does not look exactly like OS X used to look 10 years ago!'. Just some food for though. But then again, what do I know.
You know a fair bit.
We had die hard Apple fans wailing when OS X came out, not just at the lack of speed and the terrible stability (and believe me 10.0 makes iOS 8 look like an extremely stable and bug free OS), but also about the look and feel of Aqua compared to Platinum as used in OS 9.
It was labelled childish, fisher price, dumbed down, not for pro users, and many other similar labels.