By removing the home button, Apple turned iPhone into a device completely controlled by gestures. It's arguably the biggest UX change since the first iPhone, and one that was surprisingly unreported at the time. It makes the phone feel more cohesive, and the initial impression, once you learn the app switching gestures, is vaguely futuristic. FaceID works great, too, and certainly feels futuristic, though on its own it's not really a game changer. It's the integration into the buttonless UX that makes it a worthwhile feature.
(I actually wish there was also a fingerprint sensor, because the FaceID doesn't work well for contactless terminal such as the ones you find in stores -- you have to first hold the phone near the reader, then pick a card, then hold the phone at the right angle for it to recognize your face, then bring it back to the reader. Not ideal, though someone claimed the new phones would do FaceID at steeper angles, so maybe it's gotten better.)