First group is movies I haven't seen and definitely want to see. Here we have Inquest of Pilot Pirx (1978) and Dead Man’s Letters (1986).
Pilot Pirx is base on Stanislav Lem's novel which is a good recommendation on its own. Second just seems appealing in terms of story setting.
In second group is movies I've seen and would strongly recommend. Here are the products of late Soviet era, when censorship weakened. Kin-Dza-Dza! (1986) is surrealistic and post-apocalyptic style movie with marvelous actors and well written story. Zero City (1988) is better known to western movie lovers. Surrealistic story was a harsh satire on dim reality of late Soviet Union. This kind of movies you don't want to change anything in them and they don't need a "refreshing" modern remake. They good as they are.
Third group is light weight Sci-Fi made in 1970s. Here goes Moscow-Kassiopeia & Teens in the Universe and Per Aspera ad Astra (1981). They are not really interesting to watch today. The cultural reference and communist propaganda is too far to understand and appreciate even for modern generation of Russians. But, both have really interesting ideas and were technically very well done for it's time. Especially, Moscow-Kassiopeia can be turned into good young-adult movie or tv show.
Forth group movies I didn't see and most likely won't. In my case here are most of the Tarkovsky movies. I know people on the west value his work as a film director, but hear me out. When it comes to Solaris (1972) and Stalker (1979) I cannot accept his interpretation. Both stories are written by S. Lem and author himself wasn't happy how Tarkovsky interpreted his work. He almost completely destroyed original message turning it into cinematically pleasing Hollywood-style drama. I value Lem more than Tarkovsky.