Yesterday, I installed gnome-shell and managed to get it working after a little bit of trouble. Now I'm getting a kind of weird problem, which an image will explain better than my words can:
As you can see, Firefox's menu (just an example, it happens with every application) displays in the gnome-shell panel (same behavior as Unity has). Also, it seems to be under the panel, since you can't hover or click on it.
Any help will be appreciated.
You could install Gnome Tweak Tool
Then open it and turn the option on Desktop: "Have file manager handle desktop" off.