The engineers were good (if not too good, it all still stands...), but they were limited by the ideology. The city planning and the architecture were at the ideology's service. For instance, rarely did buildings have ground-level spaces for commerce and services; after all, any form of entrepreneurship was discouraged by the economic system, so there was no official need for cafes at every corner. The streets were made wide to allow for easy troops transfer and make it harder for any rebels to create barricades. Some streets were shifted by a few meters to obscure a view of churches and other historic landmarks which could provoke unrighteous thinking.
I heartily recommend Ryszard Kapuscinski's 'Imperium' (it's available in English) if you want to learn more about the Soviet Union in general and different cultures inhabiting it at the time. A lot of spot-on analysis of how the system worked. Brilliant documentary writing, too.
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.
One of the most visually offensive things about a lot of communist architecture is top-heaviness. It's not just a grey block of filthy concrete, it's a grey block of filthy concrete that looks like it's about to crush you.
