Recs.
Updated
SpecsUpdate
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.
Cons
Con Extension system is weakly integrated into the environment
Backward compatibility is not guaranteed and extensions seems like second class citizens in the GNOME environment.
Con Native Gnome dock isn't scalable
The native Gnome dock isn't scalable, which means if you want to change its size you have to download a customized theme for the shell and hope it has the appearance you want. Honestly again just like the icon issue it wastes way too much of the screen on high resolution monitors.
Con Full screen start menu
This may be fine if your screen is really small, but on modern fullhd desktop it looks ugly and distracting. In addition to very ineffective display of items on screen - much more could be placed on one screen if there were less empty space around and between icons
Con Longtime support is hard since every few years GNOME changes its own standards
Everytime something is complete GNOME breaks itself:
Icon naming changes almost every 3 years : once gtk icons were named stock_edit then gtk-edit then edit-edit and currently edit-edit-symbolic
- App icons change also every few years currently they get renamed to an android like scheme eg: org.gnome.Photos.svg instead of gnome-photos.svg however this breaks all common standards esp. since filenames on linux are case sensitive.
GNOMEShell extension also break on almost every release.
Currently Gtk3 has been stabilized however they are already working on GTK4 and 5 so in the worst case your desktop will need to run and support 4 GTK-toolkits at the same time.
Con Icon scalability and sorting
The icons in the "apps view" area don't have any additional sizes, the current ones are much too large to be effective for the screen space they use. Also, there is no native way to sort them in Gnome, only a very limited extension. Which means you're pretty much always better off using the search bar if you can.
Con Has several dead userspace features that are supplemented by community supported exstentions
Unfortunately the gnome updates often break these exstentions. An example of that would be GSConnect.
Con Default alt-tab behaviour is cute but extremely annoying for fast keyboard users
Con Some settings are not where the user would expect it
E.g. it is not possible to change the keyboard auto-repeat delay or rate from the usual All Setting > Keyboard like, for example, in Unity.
Many settings are considered "tweaks" and require installing a separate utility to adjust.
Further still, some settings are buried in a dconf database.