Its screen is the best I’ve ever used - viewing anything edge-to-edge on this phone is a delight. The best way I can describe it is by saying it looks like it has been superimposed onto the phone using CGI.
The gestures for navigating between apps are second to none. Using a home button to move around iOS feels like a chore in comparison.
The build quality is the best of any iPhone. This phone just feels great in your hand - in my opinion it is the perfect size and weight.
Face ID is good, it is not great. It does not work when you are in bed; when your phone is on a desk (with your face slightly out of the view of the scanner); or sporadically in fairly normal conditions. Touch ID is more reliable and predicatable.
Portrait + Lighting Modes are average at best. I’ve seen many people say portrait mode has improved significantly since its release. This, I am highly cynical of. Portrait mode probably wouldn’t be so disappointing if it wasn’t for the Google Pixel outperforming Apple’s offering using only one camera. Lighting modes are bad. Both effects need the absolute best lighting conditions (which are rarely available) to be any good.
Wireless charging is pretty disappointing in my opinion. I am fairly sure that this phone (and the 8 and 8 Plus) only have glass backs so that they can do wireless charging. I would swap to a stainless steel backing - for robustness reasons - in an instant. Wireless chargers are slow, expensive and awkward to use. Apple have their own proprietary charging mat coming soon which is supposed to be easier to use. But, it is going to be ridiculously expensive and it has been delayed for months.