Stalker is one my favourite films. The atmosphere created is absolutely haunting.
I recommend Geoff Dyer's book about the film, [Zona][1], as well as the [computer game][2] loosely inspired by the [book][3] that inspired the film.
[1]: http://geoffdyer.com/2012/02/06/zona/
[2]: https://en.wikipedia.org/wiki/S.T.A.L.K.E.R.:_Shadow_of_Cher...
Anyone who hasn't read Roadside Picnic should pick up the SF Masterworks version (a new translation that undoes some Soviet-era cuts).
I did find the complete absence of mention of the book source material in Zona to be peculiar... for such a close reading of the film, it seems like you have to at least mention the book.
That said, Roadside Picnic is a very atmospheric and captivating story on its own right. It really fleshes out the backstory - if you like the movie, read it.
The story about the Strugatskys' involvement in the film is interesting, actually. During principal photography, Tarkovsky had not just one, but two catastrophic incidences with his film stock, which was out of date. The Soviet film processing technology was limited compared to the rest of the world, and in fact he had to fight with the labs to convince them that the stock was bad. He had shot film for weeks, now ruined, and was running out of money, and was having an existential crisis. He managed to convince the Soviet culture ministry (or whoever it was that oversaw funding) that he was instead going to make it a two-part film, and therefore needed more money. Meanwhile, Tarkovsky was making large modifications to the original script, which was in fact fairly faithful to the novel when he started out, and moving increasingly away from the source material.
Arkady traveled to meet Tarkovsky, and worked closely with him through several iterations — which Tarkovsky wasn't happy with — before eventually convincing Tarkovsky that maybe they should just drop the science fiction stuff. He loved the idea (which he admitted he himself had been considering but didn't mention for fear of insulting the Strugatskys), and Arkady and Boris went back and wrote a kind of minimal script, mostly consisting of dialogue, that was less science-fiction-based and more abstract and philosophical. It was a breakthrough for Tarkovsky, who had felt restricted by the original material (much as he had with Solyaris), and with the authors' (mostly Arkady's; Boris seems to have been less happy with the whole ordeal) blessing finally felt free to do what he really wanted.
(For more behind-the-scenes gossip, there's more in The Films of Andrei Tarkovsky: A Visual Fugue by Vida T. Johnson and Graham Petrie [1].)
[1] http://www.amazon.com/Films-Andrei-Tarkovsky-Visual-Fugue/dp...
Tarkovsky always brought his own perspective to things; it's been ages since I read Lem's Solaris but from what I recall Tarkovsky also packed it full of Daddy Stuff that wasn't in the book.
Not such a bad thing; hushed reverence for the source material often yields movies that are no more interesting than reading the book (the obverse of the problem where directors run rampant and screw things up completely; the two best contrasting examples of this are SF Channel Dune vs Lynch Dune).
It's almost certain the makers of the game did not expect the target audience to know about the Tarkovsky film. I was expecting an intelligent game with something approaching the atmosphere or aesthetic of the film, but it's not. Far from it.