Even if I have a 64 bits-ready computer, I use for the time being 32 bits Mint release. I think it works better with Wine and more software is available, though I maybe wrong about it. So, some of my comments may not apply to your 64 bits release.
I use NVidia X Server Settings
(a deb during install). It's the only way I found on my Toshiba laptop to control brightness.
MGSE is default for Linux Mint 12 Lisa.
MGSE is just three extensions that can be instantly unchecked to come back to genuine Gnome Shell.
It will probably be changed for Cinnamon, a fork of Gnome Shell, for Linux Mint 13. Cinnamon session can be used right now (just 2 debs to install) and is stable. It uses a bottom panel and a classical Mint menu. For the time being, it has some few themes only but this is about to change soon.http://blog.linuxmint.com/?p=1910
Lisa is 100% compatible with Oneiric, which means you can use Ubuntu PPAs.