I don't think Yosemite is any worse than previous upgrades, but I do think that there are a LOT more users, a LOT more switchers who did the upgrade and had problems, so we see a lot more complaints. But most of them fall into the same category--WiFi (known problem), Apps that don't run (no updates), Keychain, not enough RAM, bad installs. And as I recall, most of them (not WiFi) were around with Mavericks and ML, maybe even SL. It's groundhog day...
EDIT: OH, and add in the presence of more malware (popup ads, genieo, mackeeper, etc, etc.) that new switchers tend to gravitate toward and you get the even more posts.