Ubuntu – Kubuntu 15.04 upgrade: many problems

I'll just toss here a list of problems I have with the recent upgrade to kubuntu 15.04

I'll accept that all my settings are gone because of the change of framework 4 to 5 (it would have been nice to get a big fat warning about it, or better an update/transfer method), but during the upgrade process I was asked if I wanted to keep LightDM or use the new SDDM. I chose the former, but still the latter was installed and causes problems (how do I switch between them ?)

In particular I now cannot unlock a locked screen: after I type my password, it blacks out briefly then comes back to the login screen. I can't start a new session either. After I reboot I get a crash screen about a sddm-greeter crash. Also there's no [Off]/[Reboot] buttons on the login screen.

Once logged in, if I try to log out or reboot I get plenty of crash window for various kde and sddm components and can't cleanly logout/reboot.

Something else very annoying: there's no more console in Ctrl-Alt-F2 and others. Just a black screen. Typing login/passwd blind doesn't work.