The simple answer is "never upgrade until the upgrade's been out a while"; i.e. when the complaints have subsided or maybe till the next upgrade appears with its usual bells and whistles.
I don't know about you lot, but I am getting tired of Apple's continual production of OS variations. Every now and again they produce a really good OS - if you remember PowerMacs, then OS 8.6 was far better than anything that went before, and for the OSX PowerMac, Tiger was the best version they produced; other people swear by SnowLeopard for the Intel Macs, or Mountain Lion. Since which there was Mavericks (no comment) and Yosemite, this latter seeming to me to be a reasonably decent piece of work. But they keep tinkering and putting bits in that are more suited to mobile devices than to a traditional desktop. Once upon a time you could load the system yourself from a DVD, select the bits you wanted (or deselect the bits you'd never use); now you download masses of Gb including things you might never glance at, let alone actually open.
So I'll keep Yosemite on my iMac, thankyou Apple.
Beg pardon for grumbling here, Matthias, but there are times you feel like screaming at THEM, and they just don't listen!