After installing Ubuntu 18.04, i have several small issues with new Gnome desktop, most of it i solved with plugins. But i decided to switch back to Unity desktop as for a while until i am ready to Gnome desktop.
To install Unity Desktop in Ubuntu 18.04, run
sudo apt install ubuntu-unity-desktop
You will be asked to select display manager. Select lightdm.
To make it look like Ubuntu 16.04, i copied old wallpaper used by Ubuntu 16.04
sudo cp /backup/backup-os/usr/share/backgrounds/warty-final-ubuntu.png /usr/share/backgrounds/warty-final-ubuntu.png
