I know there are some terrific fixes going around here for those with slow presentations of their desktop; but one of these two is what permanently worked for me:
LightDM doesn't appear
This can commonly happen when your system boots so fast that LightDM service is started before your graphics drivers are properly loaded. If this is your case, then you'll want to add the following config to your lightdm.conf file:
[LightDM]
logind-check-graphical=true
LightDM freezes on login attempt
You may find, as in my case, that after entering the correct username and password - and attempting to log in - that LightDM freezes. The result, of course, is that you are unable to continue to the desktop.
To fix this issue, reinstall the gdk-pixbuf packages.
You may check out this forum thread I included below:
https://wiki.archlinux.org/index.php/LightDM#LightDM_freezes_on_login_attempt