The only issues I've had with iOS 8.x have been with apps that haven't updated to be compatible with it. I think we all have some "dead" apps that the developers no longer update. But so far it has worked quite well on my iPad Mini Retina and my iPhone 6 Plus.

But it seems that each iThingie I've owned in the past has had a different set of issues, if it had any issues at all. Most have been issue free. My first iPad 1 worked well for 6 months then the screen looked like a colorful explosion of lines and dither patterns. It was replaced. My iPad Mini Retina has WiFi issues wherein it periodically slows down WiFi speed to less than 1 MBs from the usual 20 MBs. A restart takes care of that, but it is annoying. It sounds like the Air has had quite a few quirks from what I read. But I suspect it is more hardware related than iOS related.