Via Daring Fireball:
I've been a heavy user of the 3D Touch cursor control when typing and now can't live without it. The long press is an excellent way to access it for non-3D Touch devices.
Having the thesaurus built in is excellent too. I always use it on the Mac.
One of the weaknesses of the recent iOS releases were the very limited color choices during Markup. My children like to draw and scribble in Notes and were not happy when the color palette became limited to only a few colors instead of the many shades of each color.
This is useful. Many a times I've had to use the app on another phone or use iCloud on the laptop to use the feature and find lost iPhones (of course taken away by the children).
Other purported stuff include Podcast chapters (which I don't really care for) and tapbacks in notifications (which is useless in the non-US part of the world as iMessage isn't popular: Whatsapp/Telegram and the likes rule this part of the world by a mile).
I've been on the developer beta and like it so far: even the developer betas are much more stable than the initial public betas of the previous version of iOS.