The movie Stalker isn't really based on Roadside Picnic. Its set in the world created by Roadside Picnic, but heads in a completely different direction. Both are excellent in the own ways.
Sure, isn't that more or less what 'based on' means? Maybe I should have added "loosely".
Stalker and Solaris suggest Andre Tarkovsky was fascinated by the idea of inscrutable aliens.
Indeed. The Stalislaw Lem book Solaris is one of my all time favorite novels. Tarkovsky's 1972 movie of the same name (which is a pretty close retelling, as opposed to 'based on') is also a favorite movie. Quoting Wiki: "The film is often cited as one of the greatest science fiction films in the history of cinema."
I never bothered to watch the remake by some US/Hollywood company. By most accounts it's utter crap.
Incidentally, a quick rant about historical revisionism of movies. I watched the original Solaris in cinemas 3 or 4 times. Eventually I found it on DVD and bought it. Bloody hell.... In the DVD version there is about 5 to ten seconds missing from one scene. An omission that utterly subverts the entire movie, completely sapping the core strength and meaning. Totally ruined, and anyone seeing the version with that cut will fail to get what the movie is fundamentally about.
It should be criminal to do such vandalism to a great work of art. I find it hard to believe that could have been done for any other reason than to deliberately ruin the movie's power and depth. An example of the (((Destroyers))) work, those who deliberately tear down anything greater than themselves.
It's in the scene where Kris has bundled Hari onto a rocket in the station's silo. The missing seconds are from where he closes the rocket hatch, to when the rocket is launching. The cut is crudely done; one moment he's standing at the door, next moment rolling behind a control panel to shield from the rocket flames. There's no hint that something significant happened in the meantime.
I won't spoiler the movie by saying what happened. But it's deeply shaking. It's the crucial underlining to the basis of the movie - that Hari is not only a human soul, but ALSO a product of the planet Solaris. The whole tragedy and mystery of the film pivots on that moment. With it gone, the film's theme is derelict.
I'd happily murder the bastard that did that cut. Slowly.
Wish I could find an unmutilated version.