Ranked in these QuestionsQuestion Ranking
Pro Easy to use
GNOME 3 has been designed to make it simple and easy to use. Press a button to view your open windows, launch applications or check if you have new messages.
Pro Very productive
With a clean layout and well-thought keyboard shortcuts, Gnome 3 is simply the best for people looking to be productive with their computer.
Pro Online account management
GNOME 3 integrates with your online accounts, so that all your data can be accessed from the same place.
Pro Adheres to standards
Allowing for interoperability and shared technology for X Window System desktops.
Pro Does not get in the way
GNOME 3 lets you do the things you want without getting in the way. It won't bother you or badger you with demands, and it has been designed to help you comfortably deal with notifications.
Pro Great for high dpi displays
Adjustable scaling factor makes it great for high resolution laptops and far away TVs.
Pro Powerful search
A powerful search feature lets you access all your work from one place.
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.
Pro Touchscreen friendly
It works well with any touchscreen-enabled system, including newer laptops, even to the point of including a well-designed on-screen keyboard.
Pro Keyboard friendly
It's (mostly) usable without touching a mouse, so you can keep your hands on the keyboard. Shortcuts can be defined in the gnome setting. There are even more shortcuts available when using the gesetting or dconf tool, e.g. switch to desktop 5 to 9.
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 Some areas are unpolished and lack features
Some aspects are still unpolished and lack features - the gnome design team works well, but seems to not be taking input from the outside world.
Con Extension system is basically unsupported
Backward compatibility is not guaranteed and extensions seems like second class citizens in the GNOME environment.
Con It tries to reinvent the wheel
It isn't a traditional interface. Very different to adjust to.