Recs.
Updated
Specs
Pros
Pro Fallback mode offers a classic look
For people looking for older, more classic looks, Fallback mode offers just that. Ubuntu users can have this option by installing a package called "GNOME-Session-Fallback." In the future to be released GNOME 3.8, the Fallback Mode will not be included, so this is really not a long-term solution.
Pro Easy theming
Changing the look (and feel) of Gnome Shell is easy, shell theme, icon, windows and graphical elements (gtk). individually for each user. Mostly its installing some packages or unpacking some archive to a themes folder and using selecting the new theme in e.g. gnome-tweak-tool. There a lot of really good theme on deviantart.
Pro Customizable with easy-to-install extensions
With the right plugin enabled in your browser (comes with Firefox by default) you can browse and install with two clicks the many Shell Extensions available from http://extensions.gnome.org. These are listed automatically based upon the version of Gnome Shell you currently have installed.
Cons
Con No taskbar by default
GNOME doesn't have a taskbar by default, and might be confusing to people migrating from Windows for that reason. It is however possible to install it through http://extensions.gnome.org.
Con Extension system is basically unsupported
Backward compatibility is not guaranteed and extensions seems like second class citizens in the GNOME environment.
Recommendations
Comments
Flagged Pros + Cons
Con Session Manager does NOT work,
Session Manager does NOT work, and not for 8 years - yes EIGHT!. Don't get me wrong I LOVE Ubuntu-Gnome but a recent re-attempt at KDE Neon is working FLAWLESSLY, and FINALLY type in session in the search and a great GUI called Desktop Session opens up giving ALL expected options and a few more.