Change login screen to gnome-shell login

view story

http://askubuntu.com – I was just goofing around in a vm to test what would happen if I purgen unity: sudo apt-get remove --purge unity* I found that I get an startup error, but when I proceed, I got this awesome login screen: It has an sexy effect and is just the gnome style my whole pc has got. So can any one please tell me how I change the default login screen program without having to bother clicking "fix this error" on every boot? Thanks in advance. [edit] This is the error I get, and the only option that works is the, run in low settings for one session. (HowTos)