Face ID
All right. This is where the biggest sore spot is. I was very nervous about going from Touch ID to Face ID. I've had the mini now for several months, and I am used to the new dynamics of waking and unlocking the phone. Face ID is...fine. But it is not as good as Touch ID. The gap is not as big as I feared it would be, but Touch ID remains the easier interface.
With Touch ID I need one action with my thumb. Place it on the home button. From there I can press it to wake, leave it right there to authenticate, and press to go home. It might as well be one motion. And I can do it at any angle, or even in my pocket. With a Face ID phone I need to touch the screen to wake, then make sure I'm in the field of view (and looking at it: it requires your attention to be on it), and then do a swipe up from the bottom to go to the home screen. This is a step back from Touch ID.
This really messes with Apple Pay as well. Double-clicking the sleep/wake button isn't a very natural thing. Your mileage may very of course. But I find it off-putting. I am constantly accidentally taking screen shots or putting the phone to sleep. I have to think about how to hold the phone to do it successfully. Then I have to authenticate, which works well but has its limits. And only then do I tap the reader.
Tell it I want to pay -> authenticate -> tap. This is not the natural way to go about a purchase.
With Touch ID, I put to the reader FIRST. THEN I authenticate. Tap -> authenticate. Much smoother, and more natural. Apple Pay took a BIG step back going from Touch ID to Face ID. Now, fortunately, I have an Apple Watch, and I can use that without futzing with the phone. But the phone should be much better at it.
This is my biggest single problem with the 13 mini (which, really, isn't a problem with the mini specifically but with the whole design language of the home buttonless iPhones). My other problems are at the margins. This one is a real one, and I hope they improve it somehow.