Upgrading from Ubuntu 16.04 to 18.04 broke the system completely!

I tried to upgrade from Ubuntu 16.04 to Ubuntu 18.04. First, after downloading and installing of packages, I was unable to login. Login screen hanged completely and it showed Failed to authenticate. But then I logged into tty1 and then logged in Ubuntu. It was saying that I am in Ubuntu 18.04. Then it asked for reboot. So I rebooted Ubuntu from terminal. It got stuck at something like /dev/sda4 : Cleaning files. After trying for a few times, I got into tty1 and here I logged in as root user and tried to update and upgrade. But now I am getting errors like unmet dependencies and broken packages. I have done sudo dpkg -- configure -a. I don't want to do a reinstall of Ubuntu. How do I get access to my Ubuntu Desktop?

This was sort of expected, as an upgrade from 16.04 to 18.04 isn't ready yet. It should be ready by "late July".

This is from 18.04's release notes:

Upgrading from Ubuntu 16.04 LTS or 17.10

Upgrades from 17.10 will not be enabled until a few days after 18.04's release. Upgrades from 16.04 LTS will not be enabled until a few days after the 18.04.1 release expected in late July.

I was getting "Failed to Authenticate" error while on upgrade with no password field in the form, it even showed 18.04 LTS on login screen. The error was like toast message on Android devices , keeps stacking up. I thought I had no option but to wait till July like in accepted option, but the below solution worked

I hit the enter multiple times , after like 20 attempts the "Failed to Authenticate" toast vanished and the screen was back to upgrade screen which was still in progress , Seems it was asking for password for some changes or something(I dont have access to logs now)

Finally upgrade was complete some clean up did happen on obsolete packages , now tested with restarted and logoff-login, I am able to login with Bionic Beaver without issues.