I've read an article about installing gnome 3.8 and tried to install it (successfully):
sudo add-apt-repository ppa:gnome3-team/gnome3 sudo apt-get update && sudo apt-get install gnome-shell ubuntu-gnome-desktop
then, i saw that i have a problem with Unity and other default Ubuntu's behaviors:
No Icons on the desktop.
launcher not always turned on when i press on winkey
can't select squares on the desktop (the transparent orange) with the mouse.
themes have changed, font, icons, etc.
startup image has changed, also the color of grub menu (from purple to blue).
other small things.
then, i decided to uninstall gnome 3.8 and performed the steps in the article:
removed gnome3-team-gnome3 from the repository (in /etc/apt/sources.list.d)
sudo apt-get update
sudo apt-get remove gnome-shell ubuntu-gnome-desktop
didn't help, so i tried at least to change the themes with gnome tweaks, help a little bit but the fonts aren't as the default.
tried to install gnome 3 from the canonical repository (the default), there i couldn't do it. it said something about dependencies.
how do i turn back the system to the previous state?
in the end i've tried to install the old gnome-shell and after a few games this is the best i've come:
maybe this will help, this is the message i've got when i tried to install the original gnome-shell:
The following information may help to resolve the situation: The following packages have unmet dependencies: gnome-shell : Depends: libgjs0-libmozjs185-1.0 E: Unable to correct problems, you have held broken packages.