For me iOS 10 has 2 minor positive points and 2 bigger negatives. I know it has some extra abilities compared to 9, but I don't use that stuff.
positive: better event notifications in Safari (before they were visible for about 1/10 second)
positive: desktop redrawing seems faster
negative: they killed "slide to unlock" which is the best unlock method for devices without Touch ID
negative: Control Center on 2 panels is a nuisance
They need to bring back "slide to unlock", at least as an option. I guess everyone working at Apple has a new device with Touch ID so they don't notice the new unlock method is awkward for people with older devices like my iPad Air.
I have a 5C I use as an iPod. I was hesitant to upgrade it because I was worried about performance. For me I found iOS 10 actually performed as good if not better. I was surprised.
I don't like the slide to unlock on the 5C or my iPad Air since it doesn't have touch ID. I actually like the 2 panel control center now that I'm used to it. I like the notification system better again now that I'm used to it.
Overall I like the changes but nothing is that much better that it is an essential update.
Positive: It is quickier to end app. (Don't have to wait for the end of animation)
Positive: Animations are more fluid.
Negative: There is no option for notifications sort by app
Negative: Control center has two pages
Negative: Design of new notifications. I don't like it. I think iOS 9 notifications were much nicer. The same for widgets.
Negative: No slide to unlock. I like it even on Touch ID devices, when I have wet finger. And really liked slide to unlock for an alarm. I could end an alarm by slide or delay by button on the screen. Now, there are two buttons. And when I wake up I never know which is which.