The latest system update pulled GDM 3.2.x into my
~amd64 Gentoo system.
While GDM 2.x felt just right, GDM 3.x is not my thing at all. To bring back
GDM 2.x I added these masks
>=gnome-base/gdm-3 >=gnome-base/gnome-control-center-3 >=gnome-base/libgnomekbd-3 >=net-wireless/gnome-bluetooth-3 >=gnome-base/gnome-settings-daemon-3
and re-emerged the latest 2.x versions of these packages. Works.