This film falls under the the sci-fi genre, but its only the concept that invites to that categorization. In reality Stalker is an invitation to introspection, a walk to discover human's innermost fears and desires of oneself and society, a psychological debate of our perceived value. A philosophical masterpiece. Throughout the movie a series of dialogues and monologues raise various concerns that question existence itself.
Sometimes criticized for its slow pace and long takes, the film works out perfectly and is engaging for the 163min of duration. About this, Tarkovsky commented "the film needs to be slower and duller at the start so that the viewers who walked into the wrong theatre have time to leave before the main action".
This film is a great example of perseverance. There were many complications during the making of this film, but lucky us, after 5,000 meters of film and some patience, it was actually made. The film was shot three times with changes in crew and participants, changes in cinematography and script, music and pretty much everything. The Zone is portrayed in colors and the outside world is shot in a beautiful brown high-contrast monochrome.
Avoid if you are impatient and/or need dynamic cinema.