Here’s a quick overview of some of the changes in this new version:

    Window management improvements on tiling, mapping and unmapping windows, compositor’s window groups and tracking of full screen windows
    Improved out of the box touchpad support (edge-scrolling and two-finger-scrolling can now be configured independently and are both enabled by default)
    New accessibility and sound settings (both rewritten as native cinnamon-settings modules)
    Battery powered devices can be renamed
    Different favorite applications can now be set for plain-text, documents and source code files
    Panel launchers now include application actions
    Animation effects are now enabled by default on dialogs and menus
    Favorites and system options can now be disabled in the menu applet
    The photo-frame desklet now also scans subdirectories
    Improved support for GTK 3.20, Spotify 0.27, Viber

The Cinnamon 2.6 update is quite significant with support for systemd, panel support for multiple monitors, support for client-side decorations, and much more