Mirror
Structure wise it weirdly reminded me of Spike Lee's Crooklyn. Crooklyn is semi-autobiographical and constructed like series of memories which serve as a snapshot of what it's like to be black in 1970's America. Similarly, Mirror is semi-autobiographical and constructed like series of memories/dreams which serve as a snapshot of what it's like to live in the Soviet Union in the 1930's and later the 1960's.
Which is why it confuses me when I see people complain about not knowing what it's about. I don't think there's much to really get. A theme I've noticed in Tarkovsky's movies is that some things in life are unexplainable. Which I think is why he included the opening scene with the dude's stutter going away and those scenes with the girl with the hair.
Just like every other Tarkovsky movie, it is shot absolutely gorgeously. But I've come to expect that.