For audio:
* Have different volumes for different app
* Have one app play its sound on your phone and another app to another device.
* Have two apps play at the same time.
For UI:
* Hide status icons that are just always on and thus meaningless.
* Customize the navigation gestures
* Put apps into windows, split screen, etc.
* DeX for desktop environment when connected to a display -- I can even remote display to my LG TV and the magic remote can be used as a mouse pointer.
For Apps:
* Linux shell and apps (Termux) -- even X windows.
* Firefox, Chome, even Samsung Internet as browsers. Samsung's browser has some unique features for phones and tablets and I end up using it the most.
* VLC for playing downloading media easily on my devices
* Smooth integration with Windows via Phone Link -- notifications, messages, photos, remote access.
* Lots of notification customizations
I could go on. There are so many features that I have never used but that's ok -- we all need and want a different set of features. I use many of these all the time. I used to have an iPhone (and my whole family has i-devices) but I think I'd have trouble going back to such a restrictive environment. But I still fully recommend iPhones and iPads for most people.