My desktop theme becomes ugly (like windows 95) after i run "unity-greeter" from terminal. I was using Ambiance theme before the incident. I'm really frustrated right now.
I did the exact same thing, and also got ugly desktop theme...
As also mentioned in: Tragedy after login Unity from unity-greeter (lightdm) launched from processing unity, guest account desktop theme is not affected by this issue, then I thought this must be related to some files created in my home directory. I went to delete HOME/.config, it seemed fix the issue..
Be aware that this may remove other configurations you've done, like the icons on the launch bar, etc.