I was trying to find out how to try the Gnome desktop environment on Ubuntu but couldn't find much.
Here is what I did to try it, but don't do it! The best way try Ubuntu with Gnome is to just install Ubuntu Gnome. If you install the full gnome desktop you end up installing a lot of other apps and dependencies which aren't really possible to clean up again afterwards.
If you don't mind breaking your machine a bit, run:
sudo apt install gnome-desktop-environment
When prompted, choose to use gdm3 as the default.
Log out and back in again and you'll be using Gnome as the default (it's fairly similar).
Want to change back?
sudo dpkg-reconfigure lightdm
The same menu will appear as before, this time choose lightdm instead.
Reboot and you'll be back in Unity.
Don't do it.