I really like the George Clooney of Solaris also filmed by Andrei Tarkovsky, before Steven Soderbergh: that's very obviously sci-fi, and it seems to me a great film. But whatever pigeon-hole you put Stalker into you would both be increasing the risk of disappointing people and diminishing the film.
Life is precious and time is a key element. Let's make every moment count and help those who have a greater need than our own.