In my case:
- weird results of spotlight search - sometimes it shows my apps, and sometimes it doesn't (haven't figured out the rule yet)
- spotlight dedicated page at homescreen - as many of you I do not understand why they brought it back to iOS
- spotlight again - something has changed within the search engine - I have an App to control my Onkyo hifi. It is called Remote3. But when searching for it, in iOS7 I could type "onkyo" and it appeared in the results. Now it doesn't. I have to type the name of the app, which I tend to forget...
- wallpapers - I really don't like them. And why there is so few of them.
- performance not as improved as promised - I expected much more from iOS9 in this area...
- still no Siri in my native language. Because of that it is unusable - I can say "call XXX", but when the name of XXX is not an English name (and most of them aren't in my Contacts), then there is no chance that siri will understand me. The same with directions (e.g. street names), apps names, songs names etc.