Here's my report on how the installation went here, and it's mixed:
1st, Good news: The install did *not* put Unity on my system. Yay! I didn't have it, had removed it, and I was wondering if it would suddenly become default. It didn't.
I rebooted right back into Gnome-Shell, the default, and all applications and documents are intact.
Now, the bad news: NO extensions work. That means all themes are broken too, until I update all my extensions.
Is it possible that GNOME Shell is actually on your system, but that Unity has taken the default?
Did you check using terminal? If not, run this command:
Output should read:
:~$ gnome-shell --version
GNOME Shell 3.4.1