The only thing I find useful is that I can finally choose a video resolution - 720p @ 30fps or 1080p @ 30fps. (In Settings > Photos and Camera). However, this little feature could have been added to an incremental update of iOS 7...
The other useless features include a transit system search, which doesn't work in my City, and not all people live in huge cities with Transit, so who cares.
I don't need to "Find my Friends". I really don't care where they are at any given time.
Drawing in Notes? cool... but meh...
Siri - hardly use it/her.
Deep search? don't use it.
Selfies album? Really?
iCloud Drive app.. Don't use iCloud. Google Drive/Docs/Photos are much more useful, and Google Docs app doesn't use as much storage space as Pages.
Now - I'm on an iPhone 5S, so things like force touch or live photos won't help me out.
The new font? No big deal. Keyboard upper/lower case? Again, could have been in an incremental update instead of being a major feature. Feel weird typing on lower case letters.
Conclusion? If you're worried about the upgrade process, skip iOS 9, wait to see if iOS 10 is worth it. As for me, if there's nothing major in iOS 10, I might be switching teams next time around.