Ubuntu already comes with Gnome 3, don't get all confused. Unity is compiz plug in, the underlaying environment is Gnome 3. The Gnome Shell is the new implementation of the Gnome 3 GUI, it's made of the regular Gnome session and the Fallback session.
Put simply Gnome Classic or Gnome Fallback Session, is the Gnome Shell without the "3D" greatness.
It is as effective as you get to work with it. Now, yes you can Uninstall Unity and just keep Gnome Shell or the use the Fallback session.
Now, I get lost when you ask if you get "more things available" more of what?.
Today after installing Gnome Shell from the Software Center in Ubuntu 12.10 my Ambience and Radiance themes got corrupted as well. I found this post on the Ubuntu Forums which lead me to the solution for the problem.
The problem seems to be that after installing Gnome Shell the default theme is Adwaita (in gnome-tweak-tool). It tells me that Adwaita is the default and before it was Ambiance. And because of this when I select the theme Ambiance some components of Adwaita persist, especially selected items in the menu bar in Gnome Classic appear as gray text on gray background.
I noticed that this, in contrast to what nils8950 said, only happens with GTK2 applications, not with GTK3 applications.
So after reading that Ubuntu Forum post, I looked at the contents of the file ~/.gtkrc-2.0 which is a hidden file in your home directory. The contents of this file looked as follows:
# -- THEME AUTO-WRITTEN BY gtk-theme-switch2 DO NOT EDIT
include "/usr/share/themes/Adwaita/gtk-2.0/gtkrc"
include "/home/serrano/.gtkrc-2.0.mine"
# -- THEME AUTO-WRITTEN BY gtk-theme-switch2 DO NOT EDIT
Which explains the problem. You can see that it loads a theme file for the Adwaita theme. You could simply remove the line that reads include "/usr/share/themes/Adwaita/gtk-2.0/gtkrc" to solve this problem, though the file clearly states DO NOT EDIT. You can see that this file was auto-written by a tool named gtk-theme-switch2. As an alternative, we can simply use that tool to change the theme back to Ambiance. If you don't already have it installed:
sudo apt-get install gtk-theme-switch
Then execute the tool from the terminal:
gtk-theme-switch2
Select Ambiance from the dropdown menu and press the Apply button. Make sure Ambiance is also selected in gnome-tweak-tool. You may need to restart some applications to see the changes (no need to reboot the system).
Best Answer
This is because you were probably using Qt applications (you didn't mention which, so can't check really), rendered in a GTK theme before. Now, they're rendered in a native theme.
Install the QtConfig tool to change this:
And run it:
Then change your setting here: