To quote Linus Torvalds, a certain version of GNOME was an unholy mess. While that might have been true in the past, GNOME has gotten better in terms of the user experience.
However, after having used Ubuntu 16.04 for 4 years, I found Unity worked better for me. The Unity tweak tool, the customizations, the workspace switching, how easy it is to manage the sound output from the notification bar generally kept me wanting more from GNOME. With GNOME, all the day to day tasks I did were quite tricky.
My shift from the default GNOME on 18.04 to Unity wasn't based on any benchmarks between how GNOME or Unity might be superior in terms of performance under the hood. I just wanted to not be learning my way around another desktop manager on Ubuntu.
This might not be much of an excuse, but I do use a MacBook Air as my work computer and the window control buttons on the left just make more sense on Ubuntu as well. Ever since GNOME became the default desktop environment in 17.10, I've disliked many of the quirks it shipped with. While I was trying Ubuntu 17.10, I kinda felt it was broken but then I came to realise that it wasn't broken, it was GNOME.
Installing Unity 7
I've installed Unity 7 by using the following commands:
→ sudo apt-get update
→ sudo apt-get install ubuntu-unity-desktop
It will install a lot of packages during the installation, hit Enter to continue. You'd be prompted to select the display manager. gdm is the default display manager for GNOME while lightdm is the display manager to go if you're installing Unity and miss the Unity login screen.
Once the installation is complete, you can reboot the computer by running sudo reboot now
From the Unity login screen that's now default, you can select another desktop environment by clicking on the Ubuntu icon.
Quickly check Unity version by running → unity --version.
Installing Unity Tweak Tool
Now comes my favorite part. Let's install the Unity tweak tool by running → sudo apt-get install unity-tweak-tool
I use the unity tweak tool to move the launcher placement to the bottom of the screen, configure workspaces, install themes and icon packs.
I've also removed GNOME from my machine completely by running:
→ sudo apt-get remove ubuntu-gnome-desktop
→ sudo apt-get remove gnome-shell
→ sudo apt-get remove gdm
You can choose to reboot now with → sudo reboot now to not see GNOME available in the list of login screen options, or you can uninstall ubuntu-gnome-desktop and it's dependencies by running → sudo apt-get remove --auto-remove ubuntu-gnome-desktop
This will remove the ubuntu-gnome-desktop package and any other dependant packages which are no longer needed.
You can also delete your local/config files for ubuntu-gnome-desktop by running → sudo apt-get purge ubuntu-gnome-desktop
*Caution! Purged config/data can not be restored by reinstalling the package.*
Finally, run → sudo apt-get autoremove to remove extra packages and dependencies no longer needed on your system.