Viy (Konstantin Yershov, Georgi Kropachyov, 1967)

A comedy of horrors

Not that Viy (Konstantin Yershov, Georgi Kropachyov, 1967) is the first-ever Soviet horror film (There's A Spectre Haunts Europe (1923)) or even the first adaptation of the Nikolai Gogol story (the first was 1909, considered lost)-- but it's the rare Soviet horror film so visually striking and tonally bizarre it's at least worth a look.

Stalker (Andrei Tarkovsky, 1979)

Alienated  

Andrei Tarkovsky's Stalker starts from an image of almost total stasis, where the camera moves past a pair of double doors to find the Stalker (a self-appointed guide into the alien-created forbidden Zone) in bed, with his wife beside him. Cut to a high angle shot of a bedstand: a water glass trembles, starts to slide; the camera glides sideways, finds the wife gazing at the bedstand, the daughter fast asleep, the Stalker trying to gauge his wife's wakefulness; glides back (past gazing wife) to the water glass in original position, as if it had never moved. 

Hard to Be a God (Trudno byt' bogom, Aleksei German, 2013)

I, Mud

Aleksei German's adaptation of the Strugatsky Brothers' 1964 novel is to put it mildly a labor of love: six years actual shooting (from 2000 to 2006), another six of post-production, with German himself dying in 2013 (the film was completed under the supervision of his wife and son); more, it's possible he'd been thinking of adapting the book through the length of his long if sparse career (five feature films, from 1967 onwards)--perhaps longer (shortly after the book's publication, if you believe some folks).