Crouton is awesome—you get a chrooted Ubuntu accessible via crosh. You have CLI access with `sudo enter-chroot` and can launch XFCE4 with `sudo startxfce4`.
I never use XFCE, but if you do, you can seamlessly toggle between ChromeOS and XFCE with a keyboard shortcut (e.g. a YouTube video playing in ChromeOS remains playing if you switch to XFCE).