Communist architecture followed the principles of communist architecture. Diversion from what the state thought was a good idea was highly un-recommended. The principles of communist architecture started off from a lot of high-minded platitudes about equality and national purpose, but in practice always translated to a monstrous block of filthy grey concrete with tiny windows that looks awful from a distance and only gets worse as you get closer.
It wasn't confined to the eastern bloc either, you can find plenty of horrible examples of a similar style dreamed up by western architects infected by similar principles; pretty much anything ugly, grey, concrete, and mid-century. They continue to blight our cities and (especially) our university campuses. But reconstruct a whole city in the same milieu, and you'll have Warsaw.