From the Arch Wiki on Gnome (where Gnome 3 is now in the main repos):
> GNOME3 comes with two interfaces, gnome-shell (the new, standard layout) and fallback mode. gnome-session will automatically detect if your computer is capable of running gnome-shell and will start fallback mode if not.
>
> Fallback mode is very similar to the GNOME 2.x layout (while using gnome-panel and metacity, instead of gnome-shell and Mutter).
>
> If you are on fallback mode you can still change the window manager with your preferred one.
You can enable fallback mode while having gnome-shell installed by opening gnome-control-center. Go to System Info > Graphics and change "Forced Fallback Mode" to ON.
Or, open a terminal and enter:
$ GSETTINGS_BACKEND=dconf gsettings set org.gnome.desktop.session session-name gnome-fallback
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