I have lived in a few 'plattenbau' and other Eastern European buildings through the years. Some of them, mostly from the 50's, are high quality by any standards. Anything newer is lacking at least in some respect (sound isolation being a very acute problem mostly, but also other issues). In the more affluent EE countries, owners invest into upgrades, but some things cannot be improved easily or at all. I have also lived in London and building quality of older/cheaper housing stock there was shockingly low compared to EE estates. Germany is much better.