This is how I installed... (NOTE the LMDE2(Betsy) repo aren't officially started so use as own risk!
1. make sure install is updated and current!
2. add the 'LMDE2(betsy) repos into your apt/sourelist
in root add a lmde2.list empty file into the folder /ect/apt/source.list.d with following lines
deb http://packages.linuxmint.com betsy main upstream import
deb http://extra.linuxmint.com betsy main
3. reload package list ;)make life easier add the mint keyring package and reload again :Pget rid of nagbox
4. install mdm (will bring some dependencies) Make MDM default DM when asked!
;)If going to use 'default mint x theme' (background slideshow) also need the packages mint-themes & mint-debian-artwork
5. in the file /ect/pam.d/mdm comment out (# start of line) the auth with gnome keyring & the line with session with gnome keyring
6.reboot PC (will get default gnomish theme) login and set theme in 'login Window' (inn menu setting or preference usually) reboot agin
Done also now uninstall lightdm ect if want
done in sparky mate, xfce (and now the ldqt dev3 release. ;)In other distros (not sparkys tho) their may be other conflicting packages (usually sometype of system-adjustments)
J.Jay