GNOME 2 was once the default desktop environment on Ubuntu and most other popular Linux distributions, from Fedora to Debian. It was a stable, simple environment. With GNOME 3 and the GNOME Shell desktop, the GNOME team made radical changes. There was no more taskbar or pop-up menu. The interface used lots of 3D effects, and performance was initially poor for many people, especially on hardware with poor 3D drivers in Linux.
Well, if you haven’t tried it in a while, GNOME 3 has improved. Performance is now good. Debian just switched back to GNOME as their default desktop, partly because its accessibility and systemd integration was better than Xfce’s, but the interface has improved enough to make those considerations possible.