Ubuntu 18.04 comes with GNOME desktop as default. As a Unity fan, if you don’t like GNOME and want to use Unity, you can absolutely do it.
In this video, I have shown how to install Unity on Ubuntu 18.04 along with the Unity greeter login screen. In the second part of the video, I also showed how to remove Unity safely and go back to GNOME.
Installation is important but so is removal procedure.
Enjoy Unity on Ubuntu 18.04 and let me know if you have any questions or suggestions.
Text form of this video can be found in this article: https://itsfoss.com/use-unity-ubuntu-17-10/