I want to replace Unity with Gnome3 in Ubuntu 14.04, I know there is a version Gnome Ubuntu but i prefer not having to reinstall Ubuntu. I guess I just must add repositories of gnome, update and install gnome-shell, but i don't know if need something more to avoid problems after with gnome extensions and other stuff. Sorry for my english.
you can install Gnome from Ubuntu software center. No need to add PPA. PPA can cause some problem with unity
Use Software Center to install Gnome 3. Then logout and click on the symbol left to your name. Select Gnome and log in. After that it should start with Gnome 3.