One scene that bothered me
Writer turns to the camera with a somber grimace and says the following:
"They're all swarming around, journalists, critics, editors--and they all demand, 'More! More!' It's a constant torment for me, a painful, shameful occupation, like squeezing out hemorrhoids. I used to think that someone would get better because of my books. In two days after I die they'll start gobbling up someone else. I wanted to change them, but it's they who've changed me."
For most of the film, I found myself asking questions for myself. In this scene, however, Tarkovsky literally turns to the audience through the Writer character and almost bluntly tells them, "See, this character represents my own plight. Get it?"
In the final scene of the movie, Stalker's wife also addresses the audience directly. I can't help but feel that this final scene would have had a much greater impact without the earlier fourth-wall-breaking scene.
It prevented a near-perfect film from being perfect.