The Tarkovski film has haunted me for 30 years so when I managed to get both the book and film simultaneously I thought I'd read the book first.
At over 3 hours the Tarkovsky film felt longer than the book, but I was absorbed and intrigued by both. John skimmed the book and dropped the film after 2 hours. He says it took the film for him to realise the book was an analogy of the Soviet state (the planet). I think there's much more to it than that and like most good things, they are not spelled out directly. Both the book and film are likely to resonate within me for ages - too soon to pronounce yet.