A more fair & balanced bunch of answers than you are going to get anywhere else. Many threads on this topic on the internet will mainly be posts from folks with issues. Not from folks that are running Yosemite just fine.
Truer words were never spoken. At a guess, I'd say that if you took EVERY post that complains about something in Yosemite -- ignoring, for argument's sake, that at least half are actually user error/ignorance -- you might have 0.1 percent all the machines currently running Yosemite.
And think like this ~ you have issues? Upgrading will only take those issues to the new operating system.
Let's try and work you through the problems first. What computer? How much free space on the hard drive? How much memory? What current operating system? Do you the free OnyX to maintain your computer, Antivirus software, Mackeeper etc. or what?