The compiz-gnome package contains a session definition which will make
display managers provide a session named 'Classic GNOME with Compiz'
that you can log in to. This session will start a GNOME 2-style desktop
(with gnome-panel, not GNOME Shell) with Compiz as the window manager.
This method is the recommended replacement for the old method of using
desktop-effects to select Compiz as the window manager for a GNOME
session.