Among the changes to find in this latest GNOME 3.12 development release are rather significant changes to the Cheese web-camera software, improved drag-and-drop with the GNOME file-roller, updated/new AppData, Glib has a new API for persistent notifications via the desktop shell, a new gapplication command-line tool, updates for the new UPower API, GNOME Control Center can now set system-wide fonts, and numerous GTK+ updates. There's also the ongoing work to better support the GNOME desktop on Wayland.
The GTK+ updates include a new notebook tab styling, a new GtkFlowBox element that is similar to GtkListBox, Broadway HTML5 back-end updates, and various other smaller updates and bug-fixes.
More details on the GNOME 3.11.2 changes can be found via the release announcement.
The official GNOME 3.12 release is expected on 26 March while the next development release (GNOME 3.11.3) is planned for mid-December.