For betas they have been good. I don't set the bar high for those. The last public beta is working really well. Yosemite reminds me of KDE in some of the stuff Apple has done.
The later versions have been decent but I installed the first public beta and really regretted it for like a month or two until it got a bit more stable.
Surely you did not disregard all the warnings on the download website and the installer itself and installed it on the main partition of your primary work computer?