UrbanSepp: To be able to play at the moment I did the following: From the new installation (727) I took the two files:
Two Point Hospital/TPH_Data/Managed/Assembly-CSharp.dll
Two Point Hospital/TPH_Data/Managed/Assembly-CSharp-firstpass.dll
and saved them. Uninstalled the game, reinstalled the old 726 version, and copied those two files in there. Now the game can load my old save, I can build rooms and I have a working overview. It is by no means a fix but at least you can have fun with the game and enjoy your well earned weekend until they provide another update.
So happy I read this forum before getting the update. After reading the update breaks the game, I'm going to wait until there is yet another update. So sad the update caused so many other programs that rendered it unplayable unless you install the previous version.
Oddly in my library it does not even show up as being updated. I checked my offline installer it is 726 and the new one there in the library is 727. I guess I need to wait for 728 and then wait to see what people on here says before daring to try it. :'(