Not so much a gimmick, as much as something that seemingly went extinct that I miss: rear fingerprint sensors. I loved them on my Nexus/Pixels, and the in-screen one on my 6a is way less consistent and convenient.
Also it flashbangs me when I try to unlock my phone at night.
Pixel 2 XL here, the rear fingerprint scanner on this is the only fingerprint scanner on any of my devices that works flawlessly, every time. Why on earth would they remove this???