Gnome-core on Debian

Apt nowadays, fairly annoyingly, installs "recommended" packages by default. It presumably wants to pull a few dozens of packages. You may skip this behaviour once with the switch --no-install-recommends, or permanently by putting the following into /etc/apt/apt.conf:

APT::Install-Recommends "false";

FWIW, I'm getting roughly 252 MB of packages on my non-X installation for a no-recommendations gnome-core. You might want to find a different desktop environment to install if that is a problem (or you can get by with a window manager alone -- a choice often overlooked).