iOS 10 is out and you should install the update.
Per-conversation read receipts in Messages
I've complained many times about how one is forced to tell people that they've seen messages in various platforms. At least before version 10, you could turn it off for Messages. In my opinion, sharing whether or not one has seen a message can share a lot of intimate information that they may not want shared, especially with strangers. I've always thought that, for close friends, I'd want to share if I've read something, but not to the general public. Now you can do that!
Emoji suggestions and hot-swapping
As one is typing, they are given three suggested words. Now, one of this words could be an emoji to replace the word you just typed.
Also, once one had typed something and switches to the emoji keyboard, words that have known emoji alternatives are highlighted, and can be tapped to make the replacement.
Sadly, this is just in Messages — for now? — but since Messages is one of the apps that I type the most in, and where I probably use the most emoji, this is okay.
With the redesign of Maps, it's been given a much cleaner, more intuitive interface, and is much easier to use with one hand between your legs, hiding the phone while you drive.
My favourite little addition is showing the temperature and current weather conditions in the corner of the screen. This especially is nice when you're looking at the location you're headed, especially if you're in mountainous or otherwise fickle-weathered regions.
It also does a better job of doing things like suggesting directions to your next calendar event and such.
If you want a full, real review of iOS 10, Nick wrote a great one. Go read it while your devices update.