This is a good point and, imho, one of the reasons GNOME and KDE are
more widely used - I remember using KDE 0.0.2 or whatever early
version they had, and I could _use_ it. It had a window manager, a
panel and a file manager that crashed every time I dragged something
to the trash. But I could use it.
...
As for starting in GDM, there is no "GNUstep" environemtn in itself. I
have built myself a gnustep.desktop (I just copied and modified
kde.desktop) I put in the gdm Sessions/ directory along with my kde
and gnome sessions, and a gnustep-session script started by the Exec=
line in gnustep.desktop(kinda like gnome-session) that starts: