Parajanov's works are also incredible. A lot of his stuff was not "acceptable" in the U(kr)SSR because of their regionalism and stark non-realist aesthetics, but Shadows of Forgotten Ancestors is a fascinating and gorgeous look at traditional Ukrainian folktale and visual culture.

If you like Hard to Be A God, you should check out Aleksei German's other films, especially Khrustalyov, My Car! from 1998, which is nominally a comedy film, but plays much more like a surrealist horror film that riffs endlessly on the Kafkaesque paranoia of Stalinist Russia. It would make a brilliant double feature with Iannucci's Death of Stalin from 2017, which was definitely influenced by German's film.