I would first advise you to read
https://wiki.gnome.org/Projects/GnomeShell/CheatSheet and discover useful
shortcuts.
Then see http://extensions.gnome.org for extensions to GNOME Shell. Those
extensions can completely modify the interface. GNOME Classic actually is a
set of extensions that turns GNOME Shell into a classical desktop (similar to
GNOME 2). I think the package "gnome-shell-extensions" (in Trisquel's
repository) contains them all, i.e., you need not visit
http://extensions.gnome.org to have GNOME Classic. You can use the
"Extensions" tab of "Tweak Tool" in the "System Settings" to
activate/deactivate/configure an extension.
And, sure, there are other desktop environments in Trisquel's repository:
LXDE, Xfce, KDE, etc.
