Cinnamon 2.2's release today will be part of the Linux Mint 17 release due out in May and will also work its way into other Linux distributions. Cinnamon 2.2 features a new look for its System Settings area, hot corners and HUD functionality, menu improvements, applet improvements, and HiDPI / retina display graphics support for displays with very high pixel densities.
Other improvements to Cinnamon 2.2 include A11y MouseWheel Zoom support, window opacity support, support for Client Side Decorations (CSD) via the updated GTK tool-kit, and other window manager improvements. Cinnamon 2.2 also has a lot of other smaller improvements such as better integration with GNOME on the same system, better support for RandR cloning, a new shutdown hotkey, sound improvements, and better systemd/logind integration.
More details on the Cinnamon 2.2 desktop update are detailed (along with plenty of screenshots) via the official Linux Mint blog announcement.