I've successfully installed and enabled X11 forwarding.. according to these instructions.
I first tried to connect via
> ssh -X <username@ipaddress> > gnome-session
> ** (gnome-session:4640): WARNING **: Cannot open display:
Later I found a suggestion to try
> ssh -XC <username@ipaddress> > gnome-session
I was seeing a screen, but the unity menu that normally appears on the left was not visible.
I am unclear what's wrong here, but will attempt to restart the system in a minute. I have full root access and retried with sudo. Nothing changed.