Is it easily possible in GNOME 3's gnome-shell to achieve similar appearance of windows' title and menu bars as with Unity's Globalmenu?
To answer you directly - no its not "easy" for gnome-shell to have unity's global menu.
However, there is an alpha quality gnome-shell global unity patch available (patch below).
As to redisplaying the minimize-maximize and close decoration back-into gnome-shell - just use gconf-editor and change the key shown - note the position of the close - minimize - maximize buttons
sudo apt-get install git-core valac-0.12 libvala-0.12-dev libgtk-3-dev gobject-introspection libgirepository1.0-dev libgtk2.0-dev autotools-dev automake autoconf intltool libtool
cd
mkdir -p globalmenu
cd globalmenu
wget http://gnome2-globalmenu.googlecode.com/files/gnome-globalmenu-0.9.alpha5.tar.bz2
tar -xvf gnome-globalmenu-0.9.alpha5.tar.bz2
git clone git://github.com/gnome-globalmenu/gnome-globalmenu.git
cd gnome-globalmenu
git checkout gnome-3
cp ../gnome-globalmenu-0.9.alpha5/src/{module.c,header.h,header-gtk2.h} ./src
autoreconf --force --install --verbose
./autogen.sh --prefix=/usr
make
sudo make GTK2_MODULES_DIR=/usr/lib/gtk-2.0/modules GTK3_MODULES_DIR=/usr/lib/gtk-3.0/modules GLIB_COMPILE_SCHEMAS=/bin/true install
sudo glib-compile-schemas /usr/share/glib-2.0/schemas
sudo rm /usr/share/gnome-shell/extensions/[email protected]/{metadata.json,extension.js,stylesheet.css}
cd
wget http://webupd8.googlecode.com/files/GlobalMenu-globalmenu.org.tar.gz
tar -xvf GlobalMenu-globalmenu.org.tar.gz
sudo cp [email protected]/{metadata.json,extension.js,stylesheet.css} /usr/share/gnome-shell/extensions/[email protected]/
sudo ln -sfv /usr/lib/gtk-2.0/modules/libglobalmenu-gtk2.so /usr/lib/gtk-2.0/modules/libglobalmenu-gtk.so
open GNOME Tweak Tool (install it in Ubuntu: sudo apt-get install gnome-tweak-tool) and enable the Global Menu extension
Now open Dash and search for Startup Applications
Add an entry gnome-globalmenu-manager
Complete the installation:
sudo cp ~/globalmenu/gnome-globalmenu/globalmenu.sh /etc/profile.d/
sudo chmod +x /etc/profile.d/globalmenu.sh
not tested by myself - original source and updated instructions
