I have to clarify that I am not an iOS 9 user yet. I think I started my iOS experience since 3.x or so. All the way up to iOS 7 I was no hesitater to upgrade my idevices whenever a public update was released. While there were ups and downs with all those updates, my general impression was that I did the right thing except for iOS 7. From there, I started to wait for a while before upgrading because believe it or not, quality of every release starting with 7 was NOT on par with previous ones. If you search for the forum you can definitely find a lot of thread asking how iOS 7, 8, 9 is holding up on people's devices.
Yes, a person can only represent himself only. But when you look at the data statistically, you would have an conclusion. The best example recently was that the star rating for Yosemite was only 3.5 while El Capitan is 4.5. You can pick up any review lower than 3 star of Yosemite and say the same thing I quoted here. But that doesn't change the fact that these days people are becoming more and more cautious when upgrading their idevices.