Got mine today. First impressions...
FaceID works very well and fast - tried it in bright sunshine, in the dark, wearing glasses and sunglasses. Worked fine. A few kinks but credit to Apple for this piece of technology and brave move in adopting it.
Notch - do not really notice it and does not bother me.
Lack of Home Button - adapted to the new swipe moves straight away and don't miss it.
Camera - have not tried the main camera yet but love the true depth camera set up. Portrait lighting is a bit hit and miss, however, the quality of selfie is improved and I really had a fun time with it. Really like how you can alter the portrait lighting after as well.
Screen and brightness - Excellent quality screen and really like the full screen. Not sure about the brightness levels and how much more this is than the Iphone 7/8.
Iphone Plus users - Came from a 7 plus and initially found it a bit weird using a phone which is smaller to hold. However, will get used to it over time. The IPX does feel nice to hold though.
Apps - not encountered issues yet with the layout but will need to spend more time to evaluate them.
Watching movies - High quality. Watched Spiderman Homecoming in landscape mode. Audio at full volume was good for a mobile device.
Case - you definitely will need a case or a skin because it is going to smudge like anything. Also would be concerned about the scratches that would build up.
Battery/Wireless charging - Have not purchased a wireless charger yet. Battery appears okay and tried out fast charge with my Macbook adapter. Worked well.
A few things which require attention in future updates- Wish you could see battery percentage on home screen. Not a dealbreaker but slightly annoying. Force quitting apps requires an extra step.