It seems like pretty subtle improvements, better camera, better cpu, better modems, faster FaceID. It's not anything groundbreaking.
I beg to differ. Each S phone had a major new feature. This one really doesn't have a major one. It does have minor new features like smart HDR/depth control but that can be bundled in the camera improvements that occur annually alongside speed upgrades.
3GS - Video Recording / Voice Control
4S - Siri
5S - TouchID
6S - 3D Touch (meh)
XS - ???